Carbon fabric based solar steam generation for waste water treatment
Graphical abstract
Introduction
With rapidly growing population and development of the modern society, the demand for energy and resources also increases. The rising demand for limited resources like fresh water is one of the major issues which require immediate solutions (Vörösmarty et al., 2000). In order to avoid a major water crisis around the world in the foreseeable future, practical solutions like decontamination of contaminated water are required. Distillation of contaminated water is one of the easiest methods among different available techniques to generate clean water. As solar energy is a green and renewable energy, use of solar energy for the yield of clean water by distillation of contaminated water is a sustainable solution to minimize clean water shortage (Shannon et al., 2008).
Even though the idea of clean water generation using solar distillation technique has been around since ancient times, the very low light to heat conversion efficiency of pure water hinders the growth of the idea into a practical solution. In traditional water evaporation, the water vapors are formed due to the bulk heating of the solution. When solar radiation falls upon water, the light penetrates into the solution as water is a poor absorber of light (Wang et al., 2016, Zhang et al., 2015). This is a real wastage of incident solar light and thus drastically affects the light to heat conversion efficiency of water. In recent times, researchers around the globe have demonstrated considerable success in ameliorating the efficiency by either adding light absorbing nanoparticles in water or with the assistance of self-floating, light absorbing porous membranes above water (Ghasemi et al., 2014, Huang et al., 2017, Ishii et al., 2016b, Ishii et al., 2016a, Ito et al., 2015, Jiang et al., 2016, Li et al., 2017, Liu et al., 2017, Liu et al., 2015, Mohammad Sajadi et al., 2016, Neumann et al., 2013, Xue et al., 2017, Yan et al., 2016, Zielinski et al., 2016). Since the development of membranes with high solar steam efficiencies, researchers have discovered the diverse applications of these membranes for clean water generation (Gao et al., 2016). These include the addition of TiO2 on the membrane for accelerated removal of harmful dye molecules like Rhodamine B from contaminated water and desalination of actual sea water to obtain drinkable water (Liu et al., 2016, Lou et al., 2016, Zhou et al., 2016). Recently, Yi. et al. reported a black Al-Ti-O hybrid self floating microporous membrane for photothermal desalination application. It manifested a high efficiency of 77.52% for desalination under simulated solar light irradiance (Yi et al., 2017). Li et al. designed a jellyfish-like solar steam generator that consists of porous carbon black/graphene oxide (CB/GO) composite layer (body), aligned GO pillars (tentacles) and expanded polystyrene (EPS) matrix. This assembled evaporator displayed an energy conversion efficiency of 87.5% under one-sun illumination (1 kW cm−2) and demonstrated its applicability in water desalination studies (Y. Li et al., 2017).
In this study, we first demonstrate the novel application of carbon fabric (CF) for an efficient solar steam generation. The three basic requirements for an efficient solar steam generation by a membrane are broadband optical absorption, porosity, and low thermal conductivity. Firstly, CF offers broad optical absorption of solar radiation in the wide wavelength range from visible to near infrared. Secondly, low thermal conductivity of CF ensures less thermal dissipation of heat across the fabric area which assists in concentrating the solar heat generated during steam generation. Eventually, the large porous structure of this fabric further acts as a capillary for water molecules, which constitutes as a continuous channel for the water molecules to add up at the air-water interface. CF also has an excellent thermal stability at high temperature, which makes it an ideal candidate for large-scale applications. We also present the application of CF in clean water generation. Owing to the excellent light to heat conversion efficiency and high thermal stability of CF, it has also been examined for clean water generation from contaminated water containing organic and inorganic contaminants. CF has also been tried out for removal of dye contaminants from water. The high mechanical stability of CF makes it possible to easily modify the fabric into a bifunctional membrane containing Titanium Dioxide (TiO2) nanorods on the surface called TCF. TCF displays bifunctionality by assisting in the accelerated removal of Rhodamine B molecules from contaminated water and by exhibiting solar driven interfacial water evaporation process.
Section snippets
Materials
Carbon Fabric (1071 HCB) was purchased from AvCarb, USA. All chemicals used in the present work were of analytical grade and commercially available. Tetrabutyl titanate (TBT) (98% Alfa Aesar), Titanium tetrachloride (TiCl4), Hydrochloric acid (HCl), Ethanol, Tetraethyl orthosilicate (TEOS), Acetone and Rhodamine B (RhB) were purchased from SDFCL, India.
Preparation of TiO2 nanorods on carbon fabric
Rutile TiO2 nanorods were grown on a carbon fabric by the hydrothermal method (Fang et al., 2015). In a typical synthesis, carbon fabric was
Characterization of CF
CF has a density of 1.5 gcm−3 and is denser than water. A wooden ring of low density (0.5 gcm−3) was hence used to keep the CF afloat the water at all times. The thickness of the CF was measured to be 0.09 cm and the thickness of the supporting wooden ring was measured to be 1 cm. Initially, CF was treated with concentrated nitric acid at 70 °C for an hour. CF, when treated with concentrated nitric acid, provides a more hydrophilic surface structure. Nitric acid acts an oxidizing agent which
Conclusions
In summary, a system which consists of modified Carbon Fabric (CF) was designed for efficient solar steam generation and waste water treatment. The CF demonstrated excellent light to heat conversion efficiency due to its broadband absorbance, macroporous structure and low thermal conductivity which promotes evaporation at the air–water interface and minimizes bulk evaporation of water. Thus CF is capable of absorbing all incoming solar irradiations and convert it into localized hot spots which
Acknowledgment
The authors would like to thanks SERB, Government of India (EMR/2016/003224) for financial support.
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Both the authors contributed equally.