Green synthesis of nanoparticles for varied applications: Green renewable resources and energy-efficient synthetic routes

2.1 Dextran

Dextran is a polysaccharide composed mostly of a-d-glucopyranosyl units with variable chain lengths and branching patterns. It may be used to cover a variety of metallic and non-metallic NPs as it is very biocompatible, non-toxic, and hydrophilic. It is made biotechnologically on a large scale using Leuconostoc mesenteroides and a variety of different bacteria strains. Because of its biocompatibility and biodegradability, the biopolymer is frequently used in biomedical fields due to its increased drug loading capacity in the host NPs [15]. In addition, the peptide was attached to the Dex surface by establishing an oxime bond between its alkoxyamino group and the reducing end of the Dex [16].

Banerjee et al. [17] synthesized Dex exopolysaccharide (Dex-EPS) by a geothermal spring origin Bacillus anthracis PFAB2. The Dex-EPS is used for the green synthesis of AgNPs. Currently, because environmental toxicity is a problem, experts are focusing on developing an environmentally friendly procedure. Given the risks inherent with the chemical NP synthesis, green synthesis methodologies have received a lot of interest for their long-term viability in nanomedicine and bioengineering. According to TEM analysis, the AgNP in Dex-EPS/AgNPs has a hexagonal form with a diameter of 84 nm. When compared to traditional antimicrobials, the Dex-EPS/AgNPs showed promising biocidal characteristics for both gram-positive and gram-negative bacteria, as well as several potentially dangerous fungi.

İspirli et al. [18] prepared AgNPs (10 nm) in neutral aqueous solutions (pH 7) of 0.4% w/v AgNO₃ in the presence of 0.3% v/w Dex. The mixture solution was put in 15 psi pressure and 120°C of autoclave to assist the reduction reaction of AgNO₃ using Dex as a stabilizing agent. Authors produced Dex from Weissella cibaria and studied the anti-microbial and anti-fungal activities of the obtained product of AgNPs-Dex. The obtained results show that 1 mg mL⁻¹ of AgNPs-Dex was sufficient for the anti-fungal activity against Fusarium oxysporum, Alternaria alternata, Aspergillus niger, Penicillium chrysogenum, and Aspergillus parasiticus and antibacterial activity against Staphylococcus aureus, Yersinia enterocolitica, Bacillus cereus, Escherichia coli, and Salmonella typhimurium.

Ashtiyani et al. [19] fabricated non-viral gene carriers based on Dex-stearic acidspermine (DSASP) amphiphilic polymer with validated lipid and amine conjugations that were linked with Fe₃O₄ NPs (12–18 nm) to increase target transport and shorten transfection time utilizing a static magnetic field. Non-viral gene carriers have shown significant promise in gene transport due to their low negative effects, improved bioavailability, permeability, and potential benefit of electrostatic interactions. The DSASP–pDNA/MNPs showed substantial pDNA condensation, resistance against DNase destruction, and significant cell survival in HEK 293T cells. In the presence of a high stearic acid content in DSASP polymer, another efficient factor in polymer size rate that leads to greater DNA condensation is the presence of stearic acid. Zhao et al. [20] synthesized acylated Dex-g-polyisobutylene (AcyDex-g-PIB) graft copolymers with varied branch lengths (Mn, PIB, 2,600–5,800 g mol⁻¹) and grafting numbers (GN, 5–28 per 1,000 Dex monosaccharide) as amphiphilic nanosphere polymer (500 nm) by nucleophilic substitution of the (−OH) and PIB-tetrahydrofuran (THF)4+ through cationic polymerization reactions. The amphiphilic AcyDex-g-PIB graft copolymers can self-assemble into nanospheres in aqueous medium, which could be used as pH-sensitive drug delivery carriers that could deliver 100% of the drug loading within 72 h at pH = 7.4. Furthermore, the antibacterial activities of AcyDex-g-PIB graft copolymers with Ag-NPs were tested against E. coli and S. aureus according to Kirby-Bauer method. The diameter of inhibition zone increases with increasing AgNPs content.

For vascular inflammation therapy, magnetic iron oxide core (Fe₃O₄; 7–10 nm) and shell of Dex with anti-inflammatory polyphenols loaded such as protocatechuic acid (PCA) were synthesized by Anghelache et al. [21]. Vascular inflammation is a key factor in the advancement of a variety of diseases, including atherosclerosis, and as a result, it has emerged as a promising therapeutic target. The obtained results confirmed that Fe₃O₄-Dex/PCA exhibited an exert activity of an anti-inflammatory at non-cytotoxic of PCA concentration (350 μM) as supported by the reduced inflammatory molecule levels such as TNF-α, IL-1β, MCP-1, IL-6, and CCR2 in activated endothelial cells (ECs) and M1-type macrophages and functional monocyte adhesion assay. In EC and monocytes, the addition of Dex on its surface has been demonstrated to reduce iron oxide cytotoxicity [22].

Esfahani et al. [23] prepared gold nanoparticles (AuNPs) coated by mercaptoacetic acid (MA-AuNPs) as a colorimetric sensor for phosphate (P) detection in drinking water. The surface plasmon resonance (SPR) effect causes the colour of AuNPs to shift from blue to red throughout the aggregation and disaggregation processes, with europium ions (Eu³⁺) functioning as the aggregating agent in this sensor. Dex is used to encapsulate the Eu³⁺ ions into a tablet form to make the detection technique more easily. As a consequence, the sensor is work simple by dissolving a Eu³⁺-Dex tablet in water and then adding MA-AuNPs to detect P colorimetrically. The detection limit of this test has been established to be 0.3 g L⁻¹ with a higher detection limit of 26 g L⁻¹, whereas the permissible limit of P in drinking water is 10 g L⁻¹.

Kokilavani et al. [24] used tyrosine and nanocomposite of Cu/Ag-Dex (26 nm) to construct a cheap colorimetric sensor for detection of Hg²⁺ in aqueous solution. Mercury is one of the most dangerous metal contaminants, posing a catastrophic hazard to the environment and human health even at very low levels.

Bevacqua et al. [25] prepared Dex–curcumin NPs of 290 nm for the delivery of anticancer drugs of prostate cancer in combination with Doxorubicin (DOXO). Functional nanocarriers that can effectively vectorize pharmaceuticals to the region of interest while also acting as cytotoxic agents are a big step forward in the hunt for effective anticancer methods with minimal side effects than the traditional chemotherapeutics. Due to NPs, DOXO release was pH-dependent, with more efficient release in acidic circumstances, and immobilizing curcumin in Dex NPs dramatically increased the curcumin efficiency. At low dosages, the IC₅₀ was reduced by half, an apoptotic impact was created, and ROS production was improved (from 67 to 134%). Finally, a synergistic relationship between NPs and DOXO was discovered, with free curcumin and Dex demonstrating further effectiveness. In various studies, Dex (DOX-NPs), loaded with doxorubicin (DOX), was utilized as a model of a well-known anticancer medication.

El Founi et al. [26] used the emulsion-solvent evaporation process to synthesize doxorubicin-loaded NPs made of a poly(o-nitrobenzyl acrylate) and Dex shell in the presence of CuBr or CuSO₄/ascorbic acid that acts as a catalyst. UV irradiation technique was applied to release DOX on the Caco-2 cell viability. After 30 s UV irradiation, the amount of DOX released was 45%, reaching even 54% after 48 h. DOX-loaded NPs were then incubated with Caco-2 cells and then irradiated for 30 s is release 31 μM of DOX, which is close to the DOX IC₅₀ value toward Caco-2 cells. In comparison, the diffusion out of DOX NPs (without irradiation) even after 48 h of incubation, does not provide such results.

Das et al. [27] created a one-pot synthesis for carboxymethyl-Dex coated (carboxymethyl cellulose [CMC]) and iron oxide (Fe₃O₄) NPs, called “CION”, that may be used for functional mapping and sensitive structural of the cerebral blood volume (CBV) using magnetic resonance imaging (MRI). When delivered intravenously, supermagnetic iron oxide NPs are potent MRI contrast agents for sensitive structural and functional mapping of CBV. Feraheme, which is developed for the therapeutic treatment of iron deficiency, has been used in multiple CBV-MRI research thus far. Due to economic and regulatory constraints, Feraheme is currently unavailable outside of the United States, making CBV-MRI procedures either inaccessible or prohibitively expensive. To overcome this problem, CION’s potential as a cross-modality research platform may be demonstrated by demonstrating simultaneous in vivo optical and MRI measurements of CBV utilizing fluorescent-labelled CION.

Several literatures used Dex to stabilize of (MRI) contrast agents. Popov et al. [28] prepare gadolinium-doped ceria nanoparticles Ce_0.9Gd_0.1O_1.95 exhibiting excellent colloidal stability due to dextran coating as MRI contrast agents with high T ₁ relaxivity (3.6 mM⁻¹ s⁻¹) and selective cytotoxicity via ROS generation to cancer cells. The viability of normal cells was not affected by the Ce_0.9Gd_0.1O_1.95 NPs, whereas a dose-dependent reduction in the MCF-7 cell viability was founded at high Dex-coated/Ce_0.9Gd_0.1O_1.95 nanocomposite concentrations of >0.3 mg mL⁻¹. This difference is most likely related to the development of mitochondrial-mediated apoptosis in cancer cells as Dex-coated/Ce_0.9Gd_0.1O_1.95 nanocomposite caused a substantial reduction in their mitochondrial membrane potential. The activation of the apoptosis mechanism in cancer cells in the presence of Dex-coated/Ce_0.9Gd_0.1O_1.95 nanocomposite was revealed by a significant increase in CD40 gene expression, indicating oxidative stress activation. In normal cells, incubation with Dex-coated/Ce_0.9Gd_0.1O_1.95 nanocomposite caused no changes in mitochondrial membrane potential while lowering ROS levels. Dex-coated/Ce_0.9Gd_0.1O_1.95 nanocomposite did not penetrate the nuclei and had no genotoxic effects in both normal and cancer cells.

Figure 2 shows the effect of Dex at concentration of 25, 100, 200, 500, and 1,000 μL as capped and stabilizing agent of the formed AuNPs as well as the identical UV-Vis spectrum of the obtained Dex-AuNPs. The TEM showed that an increase in Dex amount decreased the particle size. The average diameters of the obtained Dex-AuNPs were 25.86, 9.71, 9.59, 8.22, and 5.14 nm for adding (25, 100, 200, 500, and 1,000 μL) of Dex, respectively. The UV-Vis spectrum showed an overall blue shift of the maximum absorption peaks from 527 to 520 nm as the NP size was decreased as a result of increasing the amount of Dex. Figure 3 illustrates the γ Co-60 ray irradiation of H₂SeO₃/Dex solution at irradiation dose of 25 kGy to produce selenium nanoparticles (SeNPs) with a size of 74 nm. The colour of the 25 kGy of H₂SeO₃/Dex solution changed from colourless to orange-red, indicating that SeNPs were forming. In general, the gamma irradiation technique has been regarded as a green synthesis method capable of producing large-scale NPs [29].

Figure 2

The TEM micrographs of Dex-AuNPs with different concentration of Dex (25, 100, 200, 500, and 1,000 μL) for (a–e) samples, respectively. (f) UV-Vis absorption spectra for the corresponding AuNPs [30]. (g) Particle size distributions of the TEM images; Copyright 2018, Elsevier.

Figure 3

Photograph of un-irradiated H₂SeO₃/Dex solution and the gamma irradiation synthesized of SeNPs/Dex solutions at dose of 25 kGy and at different pHs (4, 6, and 8) ref. [31]; Copyright 2018, Elsevier.

2.2 Chitosan

Chitosan is an excellent stabilizer for the green production of metal NPs. Because of the non-covalent interactions between the surface of the metals, the metal NPs may easily aggregate in solution. However, chitosan is a steric barrier that surrounds the metal with a positive charge. The creation of homogenous metal NP solutions was enabled by the strong electrostatic repulsion between the positive-charge coated metal NPs. Chitosan has been shown to be effective for stabilizing metal NPs in several studies, as shown in Figure 4. TEM image shows porous flower-shaped palladium nanoparticles (PdNPs) synthesized by ascorbic acid reduction as green method and stabilized by chitosan. The size of the obtained flower-shaped PdNPs was discovered to be influenced by the amount of chitosan present. The flower-shaped PdNPs have great biocompatibility and stability [32]. 50 mg of vitamin C (VC) in 15 ml of water. Next, the different chitosan amount was used in concentration of 0.05, 0.067, 0.1, 0.133, 0.2, 0.4, and 0.6% to obtain different pH values of 3.01, 3.07, 3.12, 3.17, 3.26, 3.63, and 3.9, respectively. These results were lower than chitosan’s pK (usually 6.5), thus 10 mL HPdCl₄ 0.01 M was added to the chitosan solution. The resulting NPs were flower shaped in nanoscale after 2 h. Centrifugation was used to collect the samples, which were subsequently washed three times with DI and dried in a vacuum. The identical process was utilized to make PdNPs for the control group, with the exception of adding CS. The resulting PdNPs were flower shaped but varied in size, according to TEM images. The NPs made with 0.05% (m/V) CS had size of 153.7 nm, which was almost larger than those made with 0.4 and 0.6% (m/V) with size of 30 and 25 nm. The findings revealed that the appropriate NP size may be easily achieved by altering the CS concentration.

Figure 4

The TEM image of flower-shaped PdNPs, their size and shape dependence on the amount of chitosan. Ref. [32] Copyright 2019, Elsevier™.

Another example of chitosan as a size controller is green metal NP synthesis. Based on UV-visible spectroscopic data, Kalaivani et al. [33] found that the size of AgNPs was effectively decreased as the amount of chitosan is increased. Furthermore, at lower chitosan content, the size of AgNPs was noticeably increased. This conclusion was again confirmed by our recent studies where the size of metal NPs decreasing when the concentration of chitosan was increased [34]. To understand how chitosan influences the size of produced NPs, researchers proposed a hypothesis. The positively charged chitosan has a significant electrostatic interaction with the metal nuclei during the production of metal NPs in the presence of chitosan. The stronger the connection between chitosan and the metal nuclei, the higher the concentration of chitosan. This strong contact prevents precursors from attaching to metal nuclei. In the presence of a high concentration of chitosan solution, metal nuclei are unable to develop any further [35].

Modifying the characteristics of chitosan for regulating the form and size of NPs might be beneficial for environment. Harmful capping agents (e.g. CTAB, CTAC, and trisodium citrate) are commonly used as shape-directing agents for metal NPs in the chemistry technique [34,36,37]. Replacing these compounds with natural products such as chitosan is an excellent way to improve metal NP biocompatibility for long-term biomedical uses. As described in an earlier study [38], thiolated chitosan may be utilized as a soft template for the production of gold nanochains, nanoneedles, and nanoflowers. Various shapes of AuNP assemblies, including 3D microclusters, microflowers, 2D needle-like crystals 1D chains, and single crystal microcubes, could be obtained by controlling the mercapto groups density (degree of substitution) on the modified chitosan. Luesakul et al. [39] summarized the routes of SeNP self-assembly with a cubic shape using three mixture of gallic acid–folic acid–N-trimethyl chitosan (GA–FA–TMC) as follows: (1) via the electrostatic interaction enhancement between the negatively charged surface of SeNPs and the positively charged surface of the stabilizer due to N-trimethyl chitosan (N⁺(CH₃)₃), (2) via hydrophobic components of both gallic acid and folic acid, the formation of π–π stacking interaction with N-trimethyl chitosan, and (3) via the intermolecular H-bonding between the hydrophilic moieties of GA–FA–TMC. These three routes allows the self-assembly of SeNPs into cubic shape.

2.3 CMC

CMC is of an important polysaccharide stabilizer NPs because of the presence of negative charge on the CMC molecules. The charge on CMC molecules has a good influence on NP stabilization and makes colloidal stability easier to obtain [40,41]. Unlike cellulose, sodium salt of CMC is water-soluble although it is derived from cellulose molecules. CMC can be suitable in many bio-fields applications due to CMC having chemical structural stability and high mechanical properties at pH ranging from 3 to 10. A CMC solution is very viscous solution due to electrostatic interactions and intermolecular H-bonds between groups of hydroxyl and carboxylic through CMC molecules. The synergistic effect of inorganic and organic materials such as aluminium ion, glycerin, and cognac glucomannan is dependent on these electrostatic interactions. This method is suited for producing cellulose-based goods with desirable qualities that can fulfil industry’s expanding demands [42,61]. However, since intermolecular H-bondings are disrupted, this CMC polymer loses stability of its structural and viscosity at pH levels of more than 10. Because noble metals, such as Au, Pt, and Pd, cannot bind with carboxyl groups of CMC at ambient temperature, CMC is unable to create NPs of them [43], whereas CMC can stabilize FeNPs in aqueous solutions independent of temperature [44]. Nadagouda and Varma [43] established a methodology using microwave irradiation (MW; 100°C, 5 min) and CMC as a capping and reducing agent to make homogeneous CMC-stabilized noble metal salt NPs with smaller diameters. MW of aqueous solutions of noble metal salts containing suitable quantities of CMC was used to create homogenous coloured nanocomposites with varied morphologies. Unusual Cu-CMC composites displayed needle-like nanostructures in the shape of bushes, and Fe showed evenly embedded spherical NPs in the CMC matrix, whereas Ag exhibited a spherical morphology with a predominance of cube-shaped NPs. Under MW, fully dispersed FeNPs were generated in aqueous solution under vacuum (reaction time approx. 30 min), and the obtained particles is stable for 9 days in the presence of a reducing agent sodium borohydride (NaBH₄). However, PdNPs synthesized in aqueous solution at temperatures of 22, 50, 80, and 95°C using CMC as a stabilizing agent and ascorbic acid as a reducing agent to give spherical nanostructures of Pd [45]. For the trichloroethene degradation in aqueous solutions, CMC-PdNPs showed a high catalytic reactivity regardless of their size [45]. Furthermore, Pt spherical NPs were stabilized for 9 months in aqueous solutions in the presence of CMC and NaBH₄ as the reducing agent [46]. As a result, it is acceptable to conclude that spherical metal NPs were generated when CMC was added as a stabilizing agent (independent of the existence or absence of the reducing agent).

Maslamani et al. [41] prepared nanocomposite beads of CMC/CuO-NiO stabilized by CMC by following the steps. Initially, of CMC 0.5 g was dissolved in deionized water of 25 mL at temperature of 50°C with 2 h stirring to form homogenized solution of CMC. Then, 60 mg of mixed CuO-NiO (50:50) was dispersed in 5 mL deionized water and sonicated for 10 min. Then both CMC solutions were mixed and CuO-NiO dispersed at temperature of 50°C for 1 h, and then the homogeneous mixture was added dropwise into a the crosslinking solution of FeCl₃ (0.2 M) with stirring to form beads of CMC/CuO-NiO. Asghar et al. [47] used Syzygium aromaticum ethanolic buds extract as a reducing agent and CMC as a stabilizing agent in the green synthesis approach of AgNPs. The colloidal AgNPs were characteristic using a UV spectrophotometer for performed the successful synthesis of CMC-AgNPs. CMC-AgNPs UV-Vis spectrum shows numerous SPR bands at various wavelengths in the region of 400–420 nm, indicating the presence of a combination of CMC, AgNPs, and plant extract.

In order to fabricate AgNPs in aqueous solution, Khan et al. used sulfonated CMC (S-CMC) as an eco-friendly stabilizer agent [48]. The synthesis of AgNPs was investigated using UV-Vis spectra and typical SPR peak analysis. The UV-Vis spectra exhibits maximum absorbance (λ _max) at about ∼400 nm owing to SPR of (S-CMC)-AgNPs nanobiocomposites. The obtained results showed that the low S-CMC concentration leads to widen SPR bands due to a low concentration of S-CMC, and there is no redox reaction among Ag + ions by S-CMC. However, at high S-CMC concentrations, the UV-Vis spectra exhibits maximum and sharp absorbance (λ_max) at about 390 nm owing to SPR of (S-CMC)-AgNPs. Increased concentration of S-CMC as stabilizing/reducing agent accelerated the formation of AgNP, resulting in a sharp SPR band. The formation of van der Waals forces between the S-CMC groups such as carboxyl and hydroxyl and the AgNPs resulted in the stability of AgNPs into nanobiocomposites.

Raghu Babu et al. investigated the effects of CMC concentrations on the production of PbS nanocrystals [49]. According to the FT-IR analysis, the interactions of hydroxyl (–OH) and carboxylate (–COO–) groups present in the CMC molecules appear to have a substantial role in the stabilization/capping of PbS nanocrystals, TEM analysis observations revealed that PbS nanocrystals generated with a little quantity of CMC (0.01% w/v) have aggregated nanowire networks created by the assembly of PbS NPs with random morphologies. However, aggregated nanowire networks were seen in PbS nanocrystals synthesized with a high level of CMC (0.1% w/v), but they were created by the assembly of rod-shaped PbS NPs.

3.1 Xylan

Xylan, a polysaccharide made from xylose monomers, operates as a reducing agent for the production of sustainable NPs with a wide range of applications without the usage of harmful chemicals. Corn cob is an agriculture waste that generates tens of thousands of tonnes of garbage each year, but it is also an excellent source of a bioactive reducing polysaccharide, for example, xylan. Silva Viana et al. [50] used ultrasound to extract xylan from corn cob, which was verified by using NMR studies. The extracted xylan solution (10 mg mL⁻¹) was mixed with a 1.0 mM silver nitrate (AgNO₃) solution. After 24 h, the mixture colour changed to give brown suspension of silver nanoxylans (102 nm). It has been also reported that the extract of xylans from corn cobs dissolved in the solution of NaOH under ultrasonic assist by Brito et al. [51]. He and coauthors used the extract xylan as a stabilizing and reducing agent for AgNP production. Feng et al. [52] designed an electrochemical sensor based on gold-carbon dots nanocomposite Au@CQDs50 MXene for nitrite detection in water samples. The carbon dots were synthesized from polysaccharide xylan that also used as in situ green reducing agents of gold ions at alkaline media. Commonly, a single-layered graphene quantum dots (GQDs) are prepared from carbon precursors through a bottom–up strategy. Cai et al. [53] used xylan under hydrothermal conditions to fabricate a single-layered GQDs with the assistance of NaOH/urea. The self-passivated layer of xylan molecules on obtained GQDs surface displayed quantum yield of a fluorescence 23.8%. This passivated layer was destroyed and fluorescence quenching by strong oxidants ions such as Cr(vi) are attached with xylan molecules by nitrogen and oxygen functional groups. The finding results confirm the mutual oxidation reduction reactions between Cr(vi) and xylan molecules that candidate (GQDs)/xylan molecules to use as Cr(vi) detection.

Carbon quantum dots (CQDs) based on polysaccharide of xylan are also frequently used in the detecting ions applications, The majority of CQD-based sensors depend on their optical characteristics. CQDs based on xylan might be used as a dopamine (DA) sensor. Firstly, xylan compound was used as the stabilizing and reducing agent for synthesizing AgNPs and reducing graphene oxide (rGO) to give Ag@CQDs-rGO nanocomposite. Secondly, to make an electrochemical sensor, Ag@CQDs-rGO nanocomposite was placed onto a glassy carbon electrode [54]. Because of its potential utility in diagnostics, electrochemical sensing of DA is extremely important for understanding and simply treating neurochemical diseases. The linear range for monitor DA under perfect conditions was 0.1 to 300 μM, with a detection limit of 1.59 nM (S/N = 3). Finally, the suggested technique has the potential to widen the use of polysaccharide-based CQDs, and this sensor has the potential to provide a discriminative and accurate analytical platform for DA diagnostic techniques and drug evaluation.

Feng et al. [52] used the biopolymer xylan as a greener stabilizing and reducing agent dissolved in 2% NaOH aqueous solutions for producing extremely stable and evenly dispersed AuNPs. AuNPs were found to be well distributed, with diameters ranging from 10 to 30 nm, after thorough characterization. The ideal circumstance was as follows: the HAuCl₄ to xylan ratio was 1:10 (wt:wt) at temperature of 80°C, and the reaction duration was 40 min. The xylan/AuNPs composite showed extremely selective and sensitive cysteine sensing in aqueous solution, distinguishing cysteine from dozens of other amino acids, with a limit of detection of 0.57 M for cysteine. With the addition of xylan to the Au@Ag NPs, they demonstrated improved resistance to oxidation and corrosion of H₂O₂ [55]. Xylan molecules extracted from wheat bran (WB) were preserved AgNPs from oxidation and aggregation, which also formed hot spots in between NPs [56]. Harish et al. [57] extracted xylan from WB waste biomass to be used as AgNPs fabrication as following. Practically, prepared alkaline xylan solution by dissolved 25 mg of extract xylan powder in sodium hydroxide solution (49 mL of 0.2%). Then silver nitrate solution (1 mM) was added dropwise to the alkaline solution of xylan and heated at a temperature of 100°C for 30 min. The obtained of brown colour of solution indicated the silver reduction ion into AgNPs (size ranging from 20 to 45 nm).

Luo et al. [58] described a simple and environmentally friendly technique for producing extremely stable and evenly dispersed AgNPs using a polysaccharide of xylan as a stabilizing and reducing agent via the Tollens reagents of 20% ammonium hydroxides under MW. Due to the packing of xylan, the results indicated that AgNPs were well distributed with diameters of 20–35 nm. In situ reduction of AgNPs onto transparent bacterial cellulose papers have been carried out by Pourreza et al. [59]. In this method, cellulose nanofibres act as the reducing agent to produce an embedded AgNPs in a transparent sheet. According to the UV-Vis absorption spectra of the obtained AgNPs in cellulose sheet is to give very low absorbance in the pH of 6, but by increasing the pH values to 9.5, the broadening of UV-Vis absorption spectra values increased, indicating the better conversion of silver ions to AgNPs at pH 9.5. This due to the open end chains of aldehyde groups. Perez-Alvarez et al. [60] used poly(ethylenimine) to adjust the pH of cellulose solutions at basic condition to produce CuNPs that were made using fibres of cotton as reducing agents in a green synthesis technique. The novelty here, the green synthesis technique, is low-cost and eco-friendly method, and it may be used on a bigger scale NP production.

3.2 Cellulose

Cellulose is a naturally biomaterial with 1, 4 β-glycosidic linkages in the structure and outstanding physicochemical characteristics, mechanical capabilities, and water absorption capability. These biodegradable fibrous structures are harmless, have a high crystallinity, and a huge surface area, and are chemically stable. They also garnered popularity as a result of its numerous applications in a number of different fields of study, including green synthesis of nanomaterials. Heidari and Karbalaee [61] used alkaline solution (pH = 12) of nanocrystalline cellulose without any other chemical agents to in situ green and eco-friendly synthesis of AgNPs at temperature of 65°C for 30 min. The obtained results showed that the shape of AgNPs of around 20 nm is spherical on the surface of nanocellulose (35–50 nm) and demonstrated catalytic efficiency towards the removal of 4-nitrophenol and methyl orange.

This environmentally friendly method, which allows for the creation of numerous shaped noble nanostructures without the use of toxic reducing agents such as hydroxylamine hydrochloride, NaBH₄, and so on, as well as a capping/surfactant agent, and which uses the benign biodegradable polymer CMC could have a wide range of technological and pharmacological applications. The reducing end groups of cellulose nanocrystals are modified by reductive amination to immobilize the gold ions. Under three different values of pH, the reducing groups were chemically modified through reductive amination using sodium cyanoborohydride (Cn) and sodium triacetoxyborohydride (Ac) or 2-picoline-borane complex (Pc). The pH of the reaction medium was discovered to be a critical factor in the green synthesis effectiveness of reduction reactions. The amine group of the molecule is deprotonated at pH 9.2, allowing the reductive amination process to be more efficient. Because the thiol concentrations obtained with the reducing agents Ac and Pc were similar to those obtained with Cn at basic pH. It can be confirmed that at pH 9.2, which corresponds to the amine’s pK _a, all three reducing agents produced the maximum conversion [62]. As a result, topochemical reactions may be used to attack reducing end-groups in open-chain aldehyde forms, allowing for end-wise alteration of original cellulose molecules. The open-chain aldehyde is achieved in alkaline media or by another’s chemical modifications reactions of cellulose such as reactions of cellulose end aldehyde groups with 9H-fluoren-2-yl-diazomethane [63], n-conjugation of aldehydes with 4-amino-3-hydrazino-5-mercapto1,2,4-triazole [64], e carbazole-9-carbonyloxyamine [65], hydroxylamine hydrochloride [66], and sodium chlorite [67]. Compared to another reduction reactions the use of cellulosic compounds as reducing agent of ions in alkaline conditions is ecofriendly due to it has the advanced of easy process, low price and renewability.

5.1 Solvent

The interaction between atoms and solvent is dependent on the dielectric constant and polarity of the solvent and appears to have a crucial impact. Constantly, an extra solvent is associated with the atoms are produced in a uniform manner due to the atom-solvent bond energy.

The solvent dependence of absorption spectra in solutions is proof of the substantial effect of the atom-solvent interaction. For example, the wavelength maxima is blue-shifted of the UV-Vis spectroscopy of Ago and Ag²⁺ with the increasing polarity of solvent and dielectric constant [121,122]. In addition, the existence of reducing agents in the solvent has the greatest impact on particle size and dispersion; so the faster the reduction reaction, the smaller the particles obtained.

Here, the irradiated solvent is itself the reducing agent; for example, water but the ˙OH radicals are strong oxidants, and should be avoided. They can be scavenged by adding a scavenger molecule of ˙OH radicals, such as t-butanol and primary alcohol or secondary alcohol or formate ions, which produce high yield solvated electrons (e_hy) and H˙ radical, that are powerful reducing agents at ambient temperature.

Practically, the use of alcohols as solvents has strong reducing properties due to the solvated electrons, and ˙H atoms are produced primary after irradiation process. The reducing radiolytic species yield is less in low dielectric solvents such as THF or propylene glycol monomethyl ether acetate than in more polar solvents. The radiolysis of these solvents will yield cation species on the solvent + molecules that partially recombine with the hydrated electron (e_hy). At a certain irradiation dose, these solvents may produce and grow up stable AgNPs and AuNPs due to a positive charge repulsion.

It concluded that the irradiated solvent could be used as a reducing agent, and a reducing chemical is unnecessary. For example, Balcerzyk et al. [123] used irradiated aqueous acidic and neutral silver ions solutions to study the dynamics of the silver reduction in both solutions. Ten solutions of silver ion concentrations (10–150 mM) were subjected to picosecond pulse radiolysis experiments (pulse width 7 ps). The studies were conducted out in a neutral water solution and a strongly acidic phosphoric acid solution. The pump probe method was used to evaluate the AgNPs yield inside the electron pulse at varied concentrations of silver ions by measuring both the decay of the hydrated electron (e_hy) and the formation of AgNPs. The obtained results showed that at low concentration of silver ions (0.1 up to 0.8) mol L⁻¹, the AgNPs yield is high from acidic solutions than neutral solutions at the end of a 7-ps pulse. However, at high concentration of silver ions (0.12 and 0.15) mol L⁻¹, the AgNPs yield is high from acidic solutions than neutral solutions at end of a 7-ps pulse. This might be due to two reasons: (1) the formation of ion pair between the hydrated electron (e_hy) and H₃O⁺ and (2) the viscosity of phosphoric acid at high concentration of silver ions solutions ((0.12 and 0.15) mol L⁻¹) restricts the motion of hydrated electron (e_hy) for nanoseconds compared to neutral solutions.

Dey et al. [124] used irradiated 2-propanol solvent (dose rate 1.8 kGy h⁻¹) that displays strong reducing species of e_hy and (CH₃)₂C˙OH (2-hydroxyl-2-propyl radical) to take an active function in gold ion reduction. Finally, solvent radiolysis typically have a crucial responsibility in the NP synthesis.

5.2 pH

The NP size appears to be influenced by the pH, as the SPR band from the NPs tends to red-shift as the pH rises, accompanied by a loss in stability and a higher inclination to agglomerate. Ghobashy et al. studied the effect of pH (1, 5, 8, and 13) in terms of size and nanostructure of poly aniline (PAni) in DMF solvent. UV-visible spectroscopy revealed that the smallest particles of PAni NPs can easily be obtained at low pH.

The TEM images revealed that the nanopolyaniline prepared at pH 1 and pH 5 is nanosphere of 5 nm. Also, the nanopolyaniline yield is higher at pH 1 than at pH 5, which can be attributed to the electrostatic interaction among the end sites of the chloride atom in the PAni chain at pH 1. However, due to the aniline polymerization of at both pH 8 and pH 13, the polyaniline NP formation are in a rod-shaped structure, which becomes bimodal structure by the existence of both oligomeric and polymeric polyanilines [125]. Liu et al. [126] founded that copper ions solution could be oxidized when the pH of solution lower than 9. Ramnani et al. observed that the size of Ag nanoclusters was increased with increasing pH of the irradiated solution [127].

5.3 The radiation dose

Another element that influences the development rate and size of NPs is the radiation dose, which is particularly noticeable in the case of NPs. It has been shown that for low radiation doses, the resulting low reducing rate results in a fewer number of metal nuclei than metal ions.

Processes of aggregation and nucleation in the NP formation could be affected by the absorbed dose. The growth rates could be determined by probabilities of the atom collisions [128]. At low radiation dose, the unreduced ions of higher than the concentration of nucleus due to a low yield of reduction reactive species. However, at higher radiation doses, most of the dissolved ions are consumed during the nucleation and reduction process; therefore, the concentration of atom nucleus is higher than the unreduced ions concentration. As a result, at higher radiation doses, the NPs are smaller in size. Rau et al. [129] synthesized AgNPs using different gamma irradiation doses in the presence of gum acacia as a stabilizing agent. It was found that according to the UV-Vis spectroscopy as the irradiation dose increases, the intensity of AgNPs optical absorption increases with blue shifts, and this means the amount and size of AgNPs increased, respectively. It concluded that, the shape of final NP products is influenced by the reduction rate and growth of NPs during the radiolytic production of solvent, which may be influenced by changing the irradiation doses. For example, during the radiation synthesis of AgNPs at low irradiation dose (30 kGy) of gamma irradiation in the existence of PVA, when the initial rate of growth is slow, the PVA capping agent takes over, resulting in the formation of small spherical AgNP (Figure 6). By increasing the dose of gamma irradiation (100 kGy), rapid adsorption of the cross-linked chains of PVA on the face of AgNPs result in the creation of triangular nanoplates from spherical nanoplates [130].

Figure 6

TEM pictures of irradiated Ag colloids samples at various gamma doses: (a) At 30 kGy, the majority of the resulting particles are spherical and (b) triangular nanoplates dominate at 100 kGy [130]. Copyright 2016.

8.1 Solar cell

Solar conversion systems have been seen as a promising way of meeting the increasing interest for vitality among the different sustainable power sources. Three generation technologies for solar production were considered when manufacturing the first solar cell. The first-generation and second-generation solar cells depended on Si nanocrystalline wafers and composed, respectively, of thick (200–300 μm) and thin (1–20 μm) semiconductor films. As the cost of production in first-generation and second-generation solar cells is high, solar cells of the third generation were built. The concept for designing solar cells of the third generation was to reduce costs while increasing the energy conversion efficiency.

DSSCs have recently gained the attention of researchers as one type of third generation solar cells [143]. As another type of third-generation solar cells, quantum dot sensitized solar cells (QDSSC) is one of the most promising, cost-effective, and an alternative to conventional silicon cells due to its distinctive features [144]. Theoretical calculations show that QDSSCs can surpass efficiency by up to 44% due to multiple exciton generation effect. However, quantum dots in nanosized have more benefits such as high coefficient of extinction, size-dependent properties, low cost material, easy processing, and photo stability. Most of materials utilized in sun powered cells sharpened to QDs depends on cadmium nanoparticles or other harmful materials, for example, lead nanoparticles (PbNPs) and tin nanoparticles. Recently, Cd-free and low-toxic nanocrystal of CuInS₂ single core was utilized as an option in contrast to harmful QDs in QDSSCs [145]. The CuZnSnS solar cell based on nanocrystal has recently been introduced as another Cd-free and eco-friendly solar cell. The efficiency of solar cell has been improved by using the light sintering technique [146].

Zavaraki et al. [147] used novel Cd-free and low toxic colloidal binary InP and ZnP quantum dots passivated with ZnS nanocrystal as another option for potential environmentally safe QDSSCs. Such QDs were synthesized under the flow of nitrogen using hot injection technique to prevent contamination with oxygen. It is observed that ZnS-passivated InP shows down-shift in the energy from the band gap, which is responsible for wider absorption. Higher power conversion performance of InPZnS QDSSCs is due to wider absorption range and higher electron injection efficiency compared to that of single core InP NPs. Under light illumination, photogenerated electron is directly injected into the TiO₂ substrate conductive band, as the thickness of the ZnS shell is designed to be as thin as possible to allow the injected electron to TiO₂ NPs. Photogenerated hole is transferred to electrolyte to allow the reset of QDs. In quantum dot-sensitized solar cells, Green Cd-free colloidal InP and ZnS-coated InP QDs have been successfully used as sensitizers. In QDSSCS, this was to provide an alternative to highly toxic QDs dependent on Cd, Pb, and Hg. ZnS-coating was found to not only induce red-shift in the onset of absorption of InP QDs but also protect InP against moisture and electrolyte.

The compounds containing the azo groups have been commonly used in the dye-sensitive solar cell, but the use of these polymers in single-layer polymer solar cells (PSCs) is not researched. Nevertheless, azo-associated polymers can potentially result in strongly light-absorbing chromophores appropriate for use in PSCs. This possesses the ability to be used in different areas such as solar cells and sensors because of the shape, morphology, and conductivity of the synthesized polymer. The PSC was manufactured with FTO/TiO₂/PPAAB/Al structure by poly(p-aminoazobenzene) PPAAB, and the efficacy of PPAAB on the efficiency of the solar cell was investigated [148]. The polymer exhibited strong thermal stability, semi-conductive compound conductivity, and nanosheet morphology. This polymer also has a fairly high power conversion efficiency and a relatively high visible area absorption in the solar cell from 300 to 800 nm due to its nanosheet structure and an strong contact surface between the chains [148,149,150]. The [Ru(bpy)₃]^3+/2+ species currently the most common dye used in DSSCs. The photo-produced electrons can, therefore, restrict the movement of the produced Ru^II and the resulting holes in the valenus after Ru^II excitation in its LMCT (ligand-to-metal charge transfer) band. However, when dealing with Boron-doped diamond (BDD), the ruthenium dyes are not the right ones for sensitization. One potential explanation may be because of the Ru-complex HOMO’s too low position compared to BDD’s valence band edge [151,152,153].

The most frequent films used in solar cells are synthetic diamond films. A conventional diamond-based solar cell device might be made as follows: A diamond film is attached as the bottom layer on a metal sheet as the cathode, and then another sheet of electrically conducting material is put on top of the bottom diamond film, with a very small gap, between which all the air has been eliminated. It is simpler to use materials with a small bandgap in solar cells to absorb a wide spectrum of solar energy. The silicone layer absorbs the incident light while the rear side of the BDD layer is submerged in electrolytes as an anode with an electrically anti-corrosive long-term property [154]. Moreover, amorphous diamond films and diamond NP NDs demonstrate the benefit of turning heat or light into electric energy. This property allows for the use of amorphous diamond in thermal electric generators or solar cell arrays. However, despite the advantages of diamond-based solar cells, it was shown that, synthetic diamond generally has high electric resistance. Solar diamond-based cells will run too hot for manually running types of electronic devices, but there are no issues with large-scale energy converters for rooftops or solar-cell farms. Furthermore, highly doped diamonds have less clarity to visible light, which limits their applications in solar cells [155].

For the construction of solar cells, heterojunctions use C₆₀ and fullerenol (n-type), with the diamond and metal phthalocyanin derivatives (p-type). A benefit of using ND in solar cells is increase the amount of the p–n heterojunction interface. NDs were used as electron acceptor and porphyrin as electron donor to create solar systems. Photoactive reaction centres (RCs) is a novel scheme involving the use of high-performance biological units in bacteria or plants for solar energy conversion. The movement of electrons on nanocrystalline diamond anchored with functionalities of the bacterial RCs is greatly increased, thereby greatly increasing the production of photocurrent. Solar cells that use semi-conductive diamond and photo-reactive RCs functionalities as building units produce enhanced photocurrent, considered to be new types of bio solar cells. This bio solar cell’s advantages will likely be realized by the use of synthetic diamond, which is used as a flexible medium for new functionalization [156].

Based on dye-sensitized colloidal TiO₂ films, a low-cost, high-efficiency solar cell has been developed by O’Regan and Grätzel [157]. The DSSC paved the way for more energy-efficient variants such as the perovskite solar cell [158] (PSC). Figure 8 illustrates that a coating of TiO₂ NPs is formed on which dye molecules are placed in a traditional DSC (a). When sunlight contacts the dye molecules, it produces both a negative charged electron (e) and a positive charged hole (h ⁺ ). The electron absorbed to an electrode through the TiO₂ coating and is then transported to a counter electrode. Finally, the electron enters a liquid electrolyte before recombining with the hole and being reabsorbed by the dye. The electrolyte is supplemented with a hole-transporting substance in a contemporary solid-state PSC (b), and chemical constituents called perovskites serve as light harvesters. To improve the effectiveness of PSCs, gold is typically utilized as the counter-electrode material.

Figure 8

The difference between (a) the dye-sensitized solar cell (DSSC) and (b) the PSC.

8.2 Renewable energy

Nanotechnology has the ability to make inexpensive renewable energy resources greener have high efficient and high reliable. Among other renewable energy uses, NPs are used to increase wind and geothermal power generation and hydrogen fuel cells. Solar thermal energy storage can also be enhanced by using NPs. The topic of renewable energy is becoming increasingly relevant due to increased demand for electricity, volatility in the oil prices and environmental problems. New energy-generation technologies, such as solar and wind technologies, have tremendous potential to reduce our reliance on energy generation systems that are on demand in real time. These current generation systems, however, are intermittent and sporadic; so, new types of effective, on-demand, energy storage systems are required to leverage green generation technologies to the maximum. Such technical demands drive the need for advanced electrochemical storage devices for electricity. There are two basic ways of storing or harnessing the energy that is contained in chemical bonds. The first is to sever the bonds, by means of a chemical or thermal process, and then capture the energy emitted in the form of heat and put it into practice [159]. By breaking those bonds and creating new bonds, a heat engine can absorb the energy that is stored in chemical bonds, and then use the excess energy that is produced from that process to do work. Therefore, as the heat energy taken from the source (the high-temperature tank) cannot be used to lower the temperature of the sink (the hypothermic tank) more than it already is, the amount of heat available to work will be limited by the energy difference between the source and the sink.

The absolute limit to engine output is determined by the temperature difference between the heat source and the heat sink. The ignition temperature in air for fuel is roughly 542 K. Assuming that the heat source is similar to that temperature, a heat engine’s ideal maximum efficiency will be about 49%. Although this may seem fairly small, there is, however, a loss of energy in the form of heat being transmitted to the atmosphere (i.e. the walls) through convection, solid-state conduction, and the friction associated with piston movement. This energy loss decreases the kinetic energy of the gas particles generated from the combustion of the fuel, and the heat energy also increases the temperature of the sink/surroundings (the engine), thus the actual amount of work that can be achieved by gas expansion is further reduced. Conventional heat engines can also be used to produce electricity from chemical energy through an intermediate mechanical process. Because much of the energy emitted is not used in the form of heat, a system designed to capture the energy produced, such as a fuel cell, does not suffer the same restrictions as a Carnot heat engine on its operating capacity [159].

There are four major factors in real electrochemical devices, which decrease the device’s open cell potential and operational potential. Such major factors are (1) mass concentration/transport losses, (2) activation losses, (3) ohmic losses, and (4) internal current losses. Activation losses arise from the need to resolve the energy activation barriers associated with the charging transfer reactions to ensure that the electrochemical reaction is channelled into product formation. At low current densities, those losses would have the most important effects. Such losses can be due to either the reverse electrochemical reaction, side redox reactions with either electrolyte materials, electrolyte pollutants, functional groups on the electrode surface, or unreacted fuel that can be attributable to physical losses, depending on the nature of the charge storage or generation processes associated with the system. The third type of loss is mass transport/concentration losses, which are most prevalent at high current densities. The final type and most common source of loss in any electrical device is ohmic losses. Such form of loss occurs due to the effect of the combined resistance inside the cell (separator, electrodes, and current collectors) and the interfaces between those components on the flow of electrons. All ohmic losses are directly proportional to the current. All these losses contribute in their own way to decrease the operational voltages in electrochemical devices. As we have already presented the Cu/Zn example cell that is indicative of a battery’s operation, it may be best to continue with those cells. It operates much like a galvanic cell in the regular activity of a battery, in that electricity is produced as a result of a spontaneous chemical reaction.

The operating principles of fuel cells are similar to those batteries, in that redox processes are involved in electrical energy production. As the electricity production comes from a chemical reaction, fuel cells can be seen as acting similar to galvanic cells. At that viewpoint, with one important difference, fuel cells are like primary batteries: the electroactive species are not contained within a fuel cell but are supplied from external reservoirs. The hydrogen fuel cell is a prototype fuel cell that transforms hydrogen and oxygen straight into electricity, water, and some heat via reverse water hydrolysis. The hydrogen fuel is delivered to the anode, where it is oxidized, and the proton that results migrates to the cathode, where it is mixed with oxygen in a reduction process to generate liquid water.

Electrochemical capacitors are another method of storing energy in an electrochemical cell. It is energy storage by capability of double layers. Double layer capacitance in the form of electrostatic and electrolytic condensers has been known and exploited for several decades. These devices consist of two metal plates, which are separated by a dielectric. Electrical energy is generated by placing a charge on the electrodes (metal plates), which in turn creates a dielectric polarization between the plates. This accumulation of electrical charges contributes to the creation of an electrical field between the plates and has been traditionally referred to as dielectric storage. In parallel plate condensers, the thickness of the double layer forming between the dielectric polarized molecules and the charged plate will be limited by the distance between the parallel charged plates. Therefore, the metal plate electrodes usually have a very small surface area, meaning that plate condensers or their modern counterparts generally have storage space [160].

8.3 Self-cleaning textiles

Both sustainable consumption and production are required improved consumption efficiency and a shift in consumption habits, as well as a reduction in consumption levels. Synthetic fibres, such as nylon and polyester that account for 60% of global clothing fibre, are frequently generated from non-renewable resources and harmful chemicals. More than 900 chemicals used in clothing production have been identified by the Swedish Chemicals Agency, of that 165 are listed by the EU as very harmful to human health or the environment [161]. The EU-27 textile consumption, of clothing is 70% by weight, produces a variety of effects throughout the life cycle. The phases of development and use control impacts, whereas their respective contributions to the different forms of impacts differ greatly. Reduced availability of water has an important impact on the nuclear and thermal power plants’ hydropower and cooling [161].

In recent decades, the clothing and textile industry have globalized, driven largely by tariff liberalization and the related relocation of production to low labour-cost countries. Clothing has gotten cheaper in several European nations in the recent decade when compared to many other consumer items; in exporting countries, textile and clothing production often creates jobs [162]. In addition, to achieve environmental changes, the application of the recent developments in the manufacture of new textiles could be implemented. In the textile industry, nanotechnology has a high technological potential. Because NPs have a great area-to-volume ratio and a high surface energy, they can provide exceptional durability for textiles, resulting in a better affinity for textiles and resulting in an increase in functional durability. Furthermore, a NPs coating on textiles does not affect their scent or consumer contact. Therefore, the interest in the textile industry using nanotechnologies is increasing. The major application of this technology is a new concept for a washable and maintainable textile that may drastically improve process efficiency in terms of energy and resource use [163].

The new generation textile made through a finishing process would be capable of reducing the maintenance textile product costs, such as a significant reduction in water and chemical/detergent use, and substantially reducing the temperature needed to remove permanent stains. The new textile can be categorized as “self-cleaning textiles”: they will produce a new industrial method for processing the textile itself and washing itself. In addition, the active compounds presence on the textile would cause the persistent stains to be decomposed by applying cycles of light washing and the number of surfactants, which will result in their easy removal. Washing machines that save energy are now available would have to be built and installed to optimize the benefits of the active compounds. By using nanotechnology, realizing self-cleaning qualities on textile surfaces opens up a world of possibilities for designers new materials or new applications for existing materials. Considering the possible toxicological hazards of releasing NPs in the atmosphere, there is no guarantee that the finished product can release a harmful amount of nano-TiO₂ to the atmosphere. The capacity of the revolutionary material to be washed lightly and less regularly was checked measuring a reduction in the use of tap water. This specific environmental dimension also depends on the washing cycles number. Results demonstrate that creative textile finishing provides significant benefits in terms of water consumption reduction [161,162].

Preparing TiO₂ NPs is the focus of recent attempts to improve photocatalytic activity of TiO₂ NPs and generate self-cleaning textiles have antibacterial and antifungal. Ghobashy et al. prepared fabric of polyethylene terephthalate (PET) composite with TiO₂ NPs using gamma irradiation techniques as green synthesis route. The obtained data showed that the new fabric nanocomposite of PET@TiO₂ has a self-cleaning character, which depends on the water vapour in air and light of sun [99].

The attachment of TiO₂ NPs to two-dimensional graphene nanosheets has been characterized in several techniques. For instance, free electrons on the TiO₂ surface can be bonded to produce a TieOeC nanocomposite containing unpaired carbon atoms. Owing to the tightly conjugated graphene structure producing TieOeC chemical bonds and the removal of TiO₂ band gaps due to carbon doping, these composites optimize wavelength absorption spectrum in visible region [164].

Stan et al. [165] manufactured cotton fibres treated with rGO decorated with Fe-doped, N-doped TiO₂ NPs. Several strategies have been developed to make photocatalytic self-cleaning textiles and have antimicrobial activity under visible light, the textile was made from TiO₂ nanoparticles alone or doped with different non-metals [166,167]. The improved properties of rGO-treated fibres of cotton decorated with doped of Fe-, N- with TiO₂ NPs to be used as industrial self-cleaning textiles. Cashew nut liquid shells are proposed as a possible sustainable and green raw material for synthetic dyes [168]. Perchloroethylene (PERC) is a compound widely used in dry cleaning as a solvent, given its significant safety and environmental impacts. PERC compound was used as a solvent in professional dry cleaners. PERC has serious implications for health and the environment. In recent years, less damaging alternatives to PERC have evolved, such as hydrocarbons, green clay, vinyl acetate, and liquid CO₂, and a potential water-based wet cleaning technique has been established. Wet textile washing is gaining traction as a viable alternative to dry cleaning regarding the environmental acceptability, lack of hazardous chemicals, and satisfactory cleaning results [169].