Review on the photocatalytic activity of various composite catalysts

https://doi.org/10.1016/j.cep.2015.08.006Get rights and content

Highlights

  • Advantages of TiO2 as a photocatalyst is reviewed.

  • Improvement of band gap in TiO2 by various doping reviewed.

  • Role of the modification in the physical structure towards the photocatalytic activity of various photocatalysts are reviewed.

  • Various preparation routes on the morphology of catalysts also reviewed.

Abstract

Nano sized semiconductor photocatalysts have a great scope for removal of large organic molecules like dyes and pesticides in an eco-friendly and sustainable manner. The photocatalytic decomposition of dyeing industrial wastewater produces negligible amount of solid by products. The problem associated with the existing catalysts are, their high band gap. Doping one catalyst with other suitable metals and metal oxides will enhance the efficiency of the photocatalyst and also makes the catalyst to be active in the visible region. The photocatalytic activity of the composite catalysts were highly improved through the modification in the crystallinity, micro structures, band gap, morphology, particle size and the surface area of the catalyst. This paper reviews the recent developments in the synthesis and application of composite photocatalysts. The role of synthetic pathways on the structure and activity of composite catalyst derived from TiO2, CdS, WO3, SnS and ZnO were analyzed. This paper will be more helpful for the scientists working in the field of nano sized photocatalysis.

Introduction

The nano particle researches have progressed rapidly and successively in the recent years mainly because of the unique properties of basic elements that are brought about by altering their property at atomic and molecular levels. By virtue of these properties, nano particles have found many applications in many fields such as medicine, cosmetics, agricultural, electronics, coatings, plastics etc. Out of which, the semiconductor nano particles form an important category of materials with infinite applications in the fabrication of opto-electronic devices, photonic transducers and photo luminescent tags in biological studies. Nanotechnology involves the manipulation of matter at the atomic and molecular scale to create materials with remarkably altered new properties and is a rapidly expanding area of research with huge potential in many sectors, ranging from healthcare to construction and electronics.

In medicine, it has revolutionized specific areas in drug delivery, gene therapy, diagnostics and many areas of research, development and clinical applications. Many of the processes of the human body at cell level operate on a nano scale. By coating nano particles over special chemicals certain specific groups of cells may be targeted. For example Liver drugs can target the liver only. Nanotechnology plays a crucial role in cancer therapy. Instead of using harmful levels of drugs the patient can be treated with nano amounts of a drug targeted to the problem.

Nano materials and particles may even act as catalysts and produce better results without comparison. The particles that get converted to nano scale are transparent (copper); makes possible to burn some materials (aluminum); turns solids into liquids at room temperature (gold); insulators induced to act as conductors (silicon) etc., a material such as gold, that is inert at normal scales, may be a very good chemical catalyst at nano scales. These special features highlight nanotechnology. Nano particles are important for scavenging the contaminants in the environment. Scientists have proved a great success in using nano particles to remove polychlorinated biphenyls (PCBs), DDT and dioxin from industrial sites and arsenic, salts, trichloroethylene (TCE) etc., from contaminated water. Researches are in progress to create nano sensors that can detect and monitor pollutants with amazing sensitivity. These sensors may also detect even trace amounts of contaminants and harmful microorganisms. Sensors may be deployed around industrial zones and alert surrounding communities to detect the entry of chemicals into the groundwater.

This review critically analyses the various preparative methods on the structure of nano sized metal oxides/composite metal oxides. The applications of those nano sized catalysts in perspective with photocatalysts were also reviewed. Since the scopes of metal oxide based photocatalysts were broad, the catalysts based on TiO2, CdS, WO3, SnS and ZnO were reviewed in this manuscript.

Section snippets

TiO2 as photocatalyst

Titanium dioxide is also called as titanium(IV) or Titania, the naturally occurring oxide of titanium. It is called as titanium white if it is used as a pigment. The sources of Titania are from ilmenite, rutile and anatase. Their wide ranges of applications are, from paint to sunscreen to food coloring. The common method for the preparation of titanium dioxide is from the mineral namely ilmenite. Important application areas are paints and varnishes as well as paper and plastics.

The anatase form

CdS photocatalyst

CdS is one of the opt material for solar cells and of great interest for their practical applications in electronics and photonics. Because of the unique property of size dependent physical and chemical nature it is of the great interests for the researchers. An important semiconductor has a direct band gap of 2.43 eV at room temperature is known to be the best semiconductor and has given considerable attention by the researchers for potential applications. CdS have widespread applications in

WO3 photocatalyst

Tungsten trioxide nano particles are yellow in nature and owing to its rich yellow color it is used as a pigment in paints and ceramics. These nano particles are existing as nanofluids, dispersed, transparent, coated and high purity forms. In everyday life it is used for many applications and because of its stable nature it is mainly used in the fabrication of smart windows. In industries it is used to manufacture tungstate which is the best material to prepare X-ray screen phosphors and

SnS photocatalyst

In the modern world tin and its compounds is the potential candidate in many applications. The less toxicity and layered structural properties of SnS brings it is an important semiconductor and also the energy band gap of 1.08 eV shows application in solar cells and photovoltaic devices. Tin when combined with other metals finds many applications and among the IV–VI group semiconductors, the nano structured materials of SnS. GeS and PbS are the most important ones. Many researchers have

ZnO photocatalyst

Zinc oxide (ZnO) is a white powder and is insoluble in water. It is obtained from a mineral zincite, but mostly its main preparation depends on the synthetic methods. The industries of plastic, rubber, ceramics, glass, cement depends mainly the ZnO compound. It is a semiconductor with wide band gap energy and it belongs to II–VI group of n-type semiconductor. The photoluminescence properties of ZnO make it is good candidate for potential scintillator applications. It also has a good property of

Metal selenide photocatalyst

Simple co-reduction method under ultrasonic irradiation method was carried out by Hongmei et al. [125] to prepare Bi2 Se3 nanobelts with a width of 20–80 nm, thickness between 8 and 10 nm and a length of several micrometers. The irradiation was done for 15 h at room temperature. The ultrasonic irradiation time affected the morphology of the synthesized product because the nanoflakes formed instead of nanobelts when the stirring time is longer than 24 h. By controlling the ultrasonic reaction time,

Metal sulphide photocatalyst

Ni-doped ZnS decorated graphene composites were (GZS1h, GZS2h, GZS3h prepared by doping graphene with ZnS with a growth time of 1 h, 2 h, and 3 h, respectively) prepared by Chang et al. [130] and the authors investigated the enhanced photocatalytic hydrogen-production performance. The surface of the graphene was loaded by undoped and Ni doped ZnS for the preparation of composite photocatalyst. ZnS nanoparticles on the graphene improved the H2 production efficiency due to the larger surface area,

Metal doped metal oxides photocatalyst

Rauf et al. [134] presented the photocatalytic degradation of azo dyes using TiO2 doped with some selective transition metals. The study found to be very useful for the remediation of dye-contaminated water. A photoredox process takes place and a molecular oxygen plays an important role and other active species of radical dotO2, HO2, H2O2, OH, radical dotHO2 also involved which are generated in the sequence of the reactions. These species makes the photocatalytic process more effective and exhibited the enhanced

Nano carbon composite photocatalyst

TiO2/carboxylate-rich porous carbon composite (TiO2/CRPC) was successfully synthesized by Qu et al. [138] using low temperature carbonization process in air, the synthesized catalyst is a visible light driven photocatalyst based on the ligand-to-metal charge transfer (LMCT) process in which sodium gluconate plays an important role. The carboxylate-TiO2 complexes were formed by dispersing TiO2 nanoparticles into porous carbon containing rich carboxyalte group, and ligand-to-metal charge transfer

Conclusions

Photocatalysts are the potential candidate in nano technology due to its promise in the conversion of solar energy into chemical energy and also in the degradation of various organic pollutants. The reduction in size and doping with other suitable catalytic composites enhances the photocatalytic decomposition of complex organic molecules through reduction in the band gap of TiO2 photocatalyst with great efficiency. When CdS nano particles are doped with suitable metals, the optical band gap

References (145)

  • S.B.A. Hamid et al.

    Multiwalled carbon nanotube/TiO2 nanocomposite as a highly active photocatalyst for photodegradation of Reactive Black 5 dye

    Chin. J. Catal.

    (2014)
  • S.A.K. Leghari et al.

    WO3/TiO2 composite with morphology change via hydrothermal template-free route as an efficient visible light photocatalyst

    Chem. Eng. J.

    (2011)
  • D. Dolat et al.

    Nitrogen-doped, metal-modified rutile titanium dioxide as photocatalysts for water remediation

    Appl. Catal. B: Environ.

    (2015)
  • M. Huang et al.

    Influence of preparation methods on the structure and catalytic performance of SnO2-doped TiO2 photocatalysts

    Ceram. Int.

    (2014)
  • C. Tang et al.

    CeF3/TiO2 composite as a novel visible-light-driven photocatalyst based on upconversion emission and its application for photocatalytic reduction of CO2

    J. Lumin.

    (2014)
  • Y. Liu et al.

    PdO loaded TiO2 hollow sphere composite photocatalyst with a high photocatalytic disinfection efficiency on bacteria

    Chem. Eng. J.

    (2014)
  • A.A. Ashkarran et al.

    Double-doped TiO2 nanoparticles as an efficient visible-light-active photocatalyst and antibacterial agent under solar simulated light

    Appl. Surf. Sci.

    (2014)
  • M.J. Powell et al.

    N-doped TiO2 visible light photocatalyst films via sol–gel route using TMEDA as the nitrogen source

    J. Photochem. Photobiol. A: Chem.

    (2014)
  • C.J. Chen et al.

    P–N junction mechanism on improved NiO/TiO2 photocatalyst

    Catal. Commun.

    (2011)
  • H. Wang et al.

    Nickel nanoparticles modified CdS—a potential photocatalyst for hydrogen production through water splitting under visible light irradiation

    Int. J. Hydrogen Energy

    (2015)
  • O. Amiri et al.

    Cadmium selenide@sulfide nanoparticle composites: facile precipitation preparation, characterization, and investigation of their photocatalyst activity

    Mater. Sci. Semicond. Proc.

    (2014)
  • F. Chen et al.

    Facile synthesis of CdS nanoparticles photocatalyst with high performance

    Ceram. Int.

    (2013)
  • J. Xu et al.

    Characterization and mechanism of MoS2/CdS composite photocatalyst used for hydrogen production from water splitting under visible light

    Chem. Eng. J.

    (2015)
  • Y. Lei et al.

    Solvothermal synthesis of CdS-graphene composites by varying the Cd/S ratio

    Ceram. Int.

    (2015)
  • L. Li et al.

    Single CdS nanowire photodetector fabricated by FIB

    Microelectron. Eng.

    (2014)
  • L.V. Garcia et al.

    CdS thin films prepared by laser assisted chemical bath deposition

    Appl. Surf. Sci.

    (2015)
  • L. Wang et al.

    Noncovalent functionalization of graphene by CdS nanohybrids for electrochemical applications

    Thin Solid Films

    (2014)
  • Y. Liu et al.

    Ag/CdS heterostructural composites: fabrication, characterizations and photocatalysis

    Appl. Surf. Sci.

    (2014)
  • G. Murali et al.

    Room temperature magnetism of Fe doped CdS nanocrystals

    Phys. B: Condens. Matter

    (2012)
  • N.M. Osipyonok et al.

    Mater. Sci. Eng.: B

    (2008)
  • Q. Han et al.

    Synthesis of CdS multipods from cadmium xanthate in ethylenediamine solution

    Particuology

    (2015)
  • N.H. Patel et al.

    Study on structural, magnetic properties of undoped and Ni doped CdS nanoparticles

    Mater. Sci. Semicond. Proc.

    (2015)
  • A. Mukherjee et al.

    Synthesis of nanocrystalline CdS thin film by SILAR and their characterization

    Phys. E: Low-Dimension. Syst. Nanostruct.

    (2015)
  • B. Li et al.

    White luminescence from CdS nanocrystals under the blue light excitation

    J. Solid State Chem.

    (2014)
  • M. Priya et al.

    Novel synthesis and characterization of CdS nanoparticles

    Energy Procedia

    (2012)
  • G. Murali et al.

    Room temperature ferromagnetism in Mn doped CdS nanowires

    J. Alloys Compd.

    (2013)
  • G. Giribabu et al.

    Structural, optical and magnetic properties of Co doped CdS nanoparticles

    J. Alloys Compd.

    (2013)
  • S.A. Vanalakar et al.

    Simplistic surface active agents mediated morphological tweaking of CdS thin films for photoelectrochemical solar cell performance

    Curr. Appl. Phys.

    (2014)
  • P.A.L. Lopes et al.

    Synthesis of CdS nano-spheres by a simple and fast sonochemical method at room temperature

    Mater. Lett.

    (2014)
  • S. Padmaja et al.

    Structural and optical properties of CdS/PEO nanocomposite solid films

    Mater. Sci. Semicond. Proc.

    (2013)
  • M. Ristic et al.

    Simple route in the synthesis of CdS nanoparticles

    Mater. Lett.

    (2013)
  • N. Yavuz et al.

    Inverted structure hybrid solar cells using CdS thin films

    Sol. Energy Mater. Sol. Cells

    (2013)
  • S. Arunkumar et al.

    One-pot room temperature novel synthesis of water-soluble CdS nanotriangles via green route

    Mater. Lett.

    (2014)
  • T. Sivaraman et al.

    Effect of magnesium incorporation on the structural, morphological, optical and electrical properties of CdS thin films

    Mater. Sci. Semicond. Proc.

    (2014)
  • S. Kim et al.

    Acetone sensing of Au and Pd-decorated WO3 nanorod sensors

    Sens. Actuators B: Chem.

    (2015)
  • H. Zhang et al.

    Temperature and acidity effects on WO3 nanostructures and gas-sensing properties of WO3 nanoplates

    Mater. Res. Bull.

    (2014)
  • C. Wang et al.

    Hierarchical flower-like WO3 nanostructures and their gas sensing properties

    Sens. Actuators B. Chem.

    (2014)
  • N. Asim et al.

    WO3 Modification by synthesis of nanocomposites

    APCBEE Procedia

    (2014)
  • T. Kako et al.

    Enhancement of photocatalytic activity for WO3 by simple NaOH loading

    Appl. Catal. A: Gen.

    (2014)
  • V.V. Kondalkar et al.

    Nanobrick-like WO3 thin films: Hydrothermal synthesis and electrochromic application

    Superlattices Microstruct.

    (2014)
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