Materials Today Energy
Volume 9, September 2018, Pages 83-113
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A review on recent advances in photodegradation of dyes using doped and heterojunction based semiconductor metal sulfide nanostructures for environmental protection

https://doi.org/10.1016/j.mtener.2018.05.007Get rights and content

Highlights

  • A state of art review on heterogeneous photocatalysis for degradation of dyes.

  • This review summarizes the recent trends of semiconductor MSNSs in photocatalysis.

  • Doped semiconductor MSNSs are superior photocatalysts for dyes degradation.

  • Heterojunction semiconductor MSNSs are famous photocatalysts for dyes degradation.

  • The degradation of dyes is effected by size, surface area and amount of catalyst.

Abstract

Among the admired photocatalysts, metal sulphide-based semiconductors are most prominent photocatalysts for the degradation or decomposition of dyes in wastewater industries with low cost, environment-friendly and sustainable treatment technologies for the environmental protection. In recent years, the environmental pollution poses a serious threat to the environment and public health. To overcome the environmental pollution, doped and heterojunction based semiconductor metal sulfide nanostructures (MSNSs) are developed as photocatalysts for the purpose of photocatalytic degradation or removal of large organic dyes in an eco-friendly and sustainable fashion. This comprehensive review starts with a brief overview on dyes as pollutants, dyes classification, dyes decolorization or degradation strategies and focuses on the mechanisms involved in comparatively well understood MSNSs photocatalysts such as ZnS, CdS, CuS, Ag2S, Bi2S3, CoS, FeS, and PbS etc. It particularly discusses the recent advancements to enhance photocatalytic degradation of toxic dyes by using various MSNSs to make it a flexible and cost-effective commercial dye treatment technology. In addition, we have focused on the treatment of organic dyes using different types of MSNSs by photocatalysis and the effects of various parameters such as dopants, heterojunctions, band gap, size, light intensity, surface area, reaction time, and degradation efficiency, etc., are highlighted.

Introduction

In the past, worldwide efforts have been undertaken to use sunlight for energy production, environmental protection and water purification, in which photocatalysis plays a crucial role. The term “photocatalysis” is a potential new method capable of eliminating relatively recalcitrant organic compounds. This methodology is based on the production of electron–hole pairs by illumination with light of suitable energy, of a semiconductor material such as metal sulfide nanostructures dispersed in an aqueous medium. The turning point that allowed photochemistry to become a science on its own was recognizing the difference with that of thermal chemistry [1]. At the beginning of the 20th century, many scientists felt that irradiation was one of the many ways available for catalyzing a reaction, which is making it faster, such as heating or treating with some chemicals in a catalyzed chemical reaction. To these chemical reactions, the tag ‘photochemical’ was properly assigned, while the term ‘photocatalytic’ designated reactions accelerated by light, but maintaining the same course as the thermal reactions. The large use of the term photocatalysis and the development of a discipline specifically designed by this name began in the 1970s, with reference to two different topics. First, the oil crisis gave a strong impulse to the research of alternative energy sources, and it was hoped that man could imitate nature by exploiting solar energy for the generation of a fuel, in particular, hydrogen generation by water splitting by photocatalysis [2], [3]. The second topic is concern about increased the pollution by chemicals used and it was proposed that photocatalysis might clean up water and air avoiding the addition of further chemicals [4]. The two topics grew up from different traditions and remained separated.

In the 1970s, the photocatalytic treatment of water splitting to the generation of hydrogen on semiconductor nanoparticles was discovered. Thereafter, the development of research toward understanding the fundamental processes occurring in photocatalysis and enhancing the photocatalytic degradation efficiency of the process. Especially nanosized particles (1–100 nm) show high potential in photocatalysis process owing to their unique physical and chemical properties; and high surface to volume ratio [5]. Nanotechnology is interestingly considered to be one of the key technologies of the 21st century [6] with over 1900 consumer products that contained nanomaterials in 2017 over all technologies [7]. Nanoparticles applications are versatile and range from industrial and environmental goods like, e.g., paints, detergents, coatings or catalysts [8], to everyday products derived from food, textile [9] or cosmetic industries [10]. The photocatalyst material such as activated by light, it plays a decisive role to perform an efficient photocatalytic reaction, and therefore its selection should be done carefully to fulfill both, the appropriate electronic structure and reasonable energy of light for its photoactivation as the rate of the photocatalytic reaction is independent of the “active site” [11]. The tendency of photoactivation achieved by the unique photophysical and photochemical (photocatalytic) properties of these nano-sized photocatalysts [12], [13]. The photocatalytic degradation of the toxic compounds (dyes, pesticides, phenolic compounds etc.) using the photoactive materials in an aqueous medium is mainly depends on the band gap, surface area, amount of catalyst, and generation of an electron–hole pair. It has been observed that the surface area plays a major role in among all factors in the photocatalytic degradation of dyes, by providing a higher surface area, which leads to the higher adsorption of dye molecule on the surface of photocatalyst and enhances the photocatalytic activity.

As a typical and important class of photocatalysts, semiconductor nanostructures (MSNSs) such as metal oxides, metal sulfides and mixed compounds etc. have attracted much attention over the past decade due to their unique physical and chemical properties. In the properties of MSNSs, the quantum confinement occurs when one or more dimensions of semiconductor nanostructures are close to or smaller than the exciton Bohr radius, which is the limit size that a material maintains the continuous band structure [14], [15]. So the band gap of MSNSs can be delicately tuned by simply controlling their particle sizes without altering the chemical compositions of metal sulfide, which is the reality of binary MSNSs. Based on this, during last decades, there are a number of novel techniques that have been developed for band gap tuning of binary metal sulfide through simple artificial size control [16], [17]. The diversity of these MSNSs allows targeting of many very different properties and applications such as electrochemical devices, energy storage devices, Na & Li-Ion batteries, biological, catalysis, photocatalysis, high-performance supercapacitors and sensors & transducers (colorimetric, fluorescence and electroanalytical techniques), etc.

In semiconductor nanostructures, the metal oxides also can act as sensitizers for light-induced redox-processes due to the electronic structure of the metal atoms in chemical combination, which is characterized by a filled valence band, and an empty conduction band [18]. Upon irradiation, valence band electrons are promoted to the conduction band leaving a hole behind. These electron–hole pairs can either recombine or can interact separately with other molecules. The holes may react either with electron donors in the solution or with hydroxide ions to produce powerful oxidizing species like hydroxyl or superoxide radicals [19], [20]. Apart from the other semiconductor materials, the large numbers of semiconductors (metal oxides and complex oxides) such as TiO2 [21], ZnO [22], WO3/TiO2 [23], Nd2O3 [24], [25], Nd2Sn2O7 [26], Nd2Sn2O7-SnO2 [27], Nd2Zr2O7 [28], Ag/CeO2 [29], Ho2O3-SiO2 [30], Ho2O3 [31], [32], [33], Dy2Ce2O7 [34], [35], Dy2Sn2O7-SnO2 [36], CuCr2O4 [37], Pr2Ce2O7 [38], CoOx/BiVO4 [39], Pr6O11 [40], [41], ZrO2 [42], Nd2O3–SiO2 [43], Nd2Zr2O7–ZrO2 [44], Pr2Zr2O7 [45], and Cu2O/TiO2/Bi2O3 [46] have also been tried in combination with several oxides to serve as photocatalyst for the degradation of toxic pollutants for the environmental wellbeing.

During the past decades, as a green and sustainable technology, heterogeneous photocatalysis using semiconductors has received much attention because of its potential to address energy and environmental problems. Based on this heterogeneous photocatalysis, this comprehensive review discusses the recent developments in the synthesis and application of semiconductor MSNSs (ZnS, CdS, CuS, Ag2S, Bi2S3, CoS, FeS and PbS etc.) as photocatalysts in the field of heterogeneous photocatalytic degradation of various dyes by varying different parameters such as the size of the materials, band gap, light intensity, surface area and concentrations of dye solutions; and their interactions with aquatic contaminants as well as the harmful environmental complications. It also discusses the structure, size, and surface area of the synthesized MSNSs photocatalytic nanostructured materials and applied for the photocatalytic degradation of toxic dyes under UV, visible and solar irradiations; and their dye degradation capabilities. The knowledge gap and future research needs are also identified, and the challenges in assessing the environmental fate and transport of nanoparticles in heterogeneous systems are also discussed. This review will help the engineers and scientists in this field to understand the latest developments on MSNSs in the field of photocatalytic degradation of dyes for the environmental applications.

Section snippets

Outline of dyes

A dye may be defined as a colored and toxic substance which when applied to the fabrics imparts a permanent color and the color is not removed by washing with water, detergents or a revelation to light. It is colored because it absorbs light in the whole visible range of the spectrum at a certain wavelength. They are applied in various industries such as leather, paint, textile, printing, paper, rubber, cosmetics, plastic, pharmaceuticals and food industries [47], [48]. Furthermore, dyes can

Heterogeneous mechanism

Photocatalytic reactions proceeds through may be homogeneously or heterogeneously, but in recent years, the heterogeneous photocatalysis is far more intensively studied because of its potential use in a variety of environmental and energy-related applications as well as in synthesis of organic compounds. In heterogeneous photocatalysis, the photocatalytic reaction implies the previous formation of an interface between a solid photocatalyst (metal or semiconductor) and other medium (fluid or

Basic principles of photocatalytic degradation of organic dyes using metal sulfide nanostructures

Photocatalysis includes the basic photochemical reactions of organic dyes, organic compounds, pesticides photodegradation, disinfection of water and air, production of renewable fuels, hydrogen generation, and organic compounds synthesis. In semiconductor nanostructures, the MSNSs are usually used as efficient photocatalysts due to their capability in absorbing broad region of visible and/or UV light, the combination of electronic structure, charge transport characteristics and excited-state

Doped and heterojunction based nanosized ZnS photocatalysts

ZnS is an II–VI compound semiconductor with direct and wide band gap (3.6 eV) [97], which make it suitable as a transparent photocatalytic material in the visible region. There are two structures of ZnS, α-phase (hexagonal wurtzite structure) and β-phase (cubic sphalerite structure) [98]. It has traditionally shown extraordinary versatility, novel fundamental properties and diverse applications such as field emitters, field effect transistors (FETs), p-type conductors, photocatalysts, chemical

Conclusions

Recent developments in technology allow us to fabricate different semiconductors with large surface area and different surface functionalities for successful removal of toxic dyes. In this regard, we have discussed the recent research improvements targeting the degradation or removal of different dyes by using various semiconductor MSNSs as potential photocatalysts. These materials are modified with different functionalities such as dopants and heterostructures are prepared with improved

Future aspects

Recently, a few efforts have been made for the synthesis of high surface area, particular shape and size of the materials by incorporation of MSNSs photocatalytic materials in or on the surface of high surface area materials like zeolites, clay, silica and metal-organic framework. The advantages of these materials are that they can be easily separated from the treated water and the dangerous effect of contamination due to nanomaterials in water can be avoided. Due to the synergic effect of

Conflict of interest

The authors declare no conflict of interests.

Acknowledgements

One of the authors, Dasari Ayodhya gratefully acknowledges UGC, New Delhi, India, for the award of Senior Research Fellowship. The authors would like to thank DST-FIST, New Delhi, India for providing necessary analytical facilities and sincere thanks to the Head, Department of Chemistry, Osmania University for providing infrastructure and other necessary facilities.

Dr. Dasari Ayodhya received his M.Sc. (Physical Chemistry) degree from Osmania University, Hyderabad, India, in 2008 and Ph.D. degree in the field of Material Science from the same university in 2016. To date, he has published more than 22 research papers in reputed international journals. His current research interest comprises of green synthesis of semiconductor metal sulfide and metal oxide nanostructures using various capping agents such as plant materials (leaf extracts, gums and latex),

References (432)

  • S. Zinatloo-Ajabshir et al.

    J. Mol. Liq.

    (2017)
  • M.S. Morassaei et al.

    Adv. Powder Technol.

    (2017)
  • S. Zinatloo-Ajabshir et al.

    J. Mol. Liq.

    (2017)
  • S. Zinatloo-Ajabshir et al.

    Ultrason. Sonochem.

    (2017)
  • S. Mortazavi-Derazkola et al.

    Adv. Powder Technol.

    (2017)
  • S. Zinatloo-Ajabshir et al.

    Int. J. Hydrogen Energy

    (2017)
  • S. Zinatloo-Ajabshir et al.

    Ceramics Int.

    (2018)
  • Z. Salehi et al.

    J. Mol. Liq.

    (2016)
  • S. Zinatloo-Ajabshir et al.

    J. Colloid Interface Sci.

    (2017)
  • S. Zinatloo-Ajabshir et al.

    Ultrason. Sonochem.

    (2018)
  • S. Zinatloo-Ajabshir et al.

    J. Energy Chem.

    (2017)
  • S. Zinatloo-Ajabshir et al.

    Sep. Purif. Technol.

    (2017)
  • M.T. Yagub et al.

    Adv. Colloid Interface

    (2014)
  • M.S. Chiou et al.

    J. Dyes Pigments

    (2004)
  • R. Qadeer

    Colloids Surf. A

    (2007)
  • A. Demirbas

    J. Hazard. Mater.

    (2009)
  • W.K. Walthall et al.

    Environ. Pollut.

    (1999)
  • G.M. Shaul et al.

    Chemosphere

    (1991)
  • O. Tünay et al.

    Water Sci. Technol.

    (1996)
  • V. Etacheri et al.

    J. Photochem. Photobiol. C

    (2015)
  • Z.M. Abou-Gamra et al.

    J. Photochem. Photobiol. B

    (2016)
  • F. Wu et al.

    Appl. Surf. Sci.

    (2015)
  • H.A. Hamad et al.

    J. Environ. Sci.

    (2016)
  • S. Anandan et al.

    J. Photochem. Photobiol. C

    (2003)
  • W.Z. Tang et al.

    Chemosphere

    (1995)
  • V. Meshko et al.

    Wat. Res.

    (2001)
  • W.S. Kuo et al.

    Chemosphere

    (2001)
  • C. Galindo et al.

    Chemosphere

    (2001)
  • I. Arslan et al.

    Dyes Pigments

    (1999)
  • M. Stylidi et al.

    Appl. Catal. B

    (2003)
  • K. Tanaka et al.

    Water Res.

    (2000)
  • H. Lachheb et al.

    Appl. Catal. B

    (2002)
  • O. Carp et al.

    Prog. Solid State Chem.

    (2004)
  • V. Augugliaro et al.

    J. Photochem. Photobiol. C

    (2006)
  • X. Yang et al.

    Mater. Today Energy

    (2017)
  • P. Pizarro et al.

    Catal. Today

    (2005)
  • H. Yates et al.

    J. Photochem. Photobiol. A

    (2006)
  • S. Challagulla et al.

    Nano-Struct. Nano-Objects

    (2017)
  • A. Arques et al.

    Catal. Today

    (2007)
  • J. Zhao et al.

    Build. Environ.

    (2003)
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    Dr. Dasari Ayodhya received his M.Sc. (Physical Chemistry) degree from Osmania University, Hyderabad, India, in 2008 and Ph.D. degree in the field of Material Science from the same university in 2016. To date, he has published more than 22 research papers in reputed international journals. His current research interest comprises of green synthesis of semiconductor metal sulfide and metal oxide nanostructures using various capping agents such as plant materials (leaf extracts, gums and latex), amino acids, nucleosides, polymers, graphene-based materials and their applications towards drug delivery, heavy metal ions detection, photocatalytic degradation of organic pollutants (dyes, pesticides, nitrophenols, and industrial waste) and biological activities (antimicrobial, antiviral and anticancer).

    Dr. Veerabhadram Guttena is a Senior Professor in the Department of Chemistry, Osmania University, Hyderabad, India. He was also Former Head and Former Chairperson, Board of Studies of the same Department. He received his M.Sc. (1978) and Ph.D. (1982) in Chemistry from Osmania University. He joined as an Assistant Professor in 1983 in Department of Chemistry, Osmania University and in 1995 he was promoted as an Associate Professor in the same University. Later he was promoted as a Professor of Chemistry in 2003. He was a visiting professor at Omar Mukhtar University, Libya (2009–2010). To date, he has published more than 74 research papers in international and national journals of repute and 10 students obtained their Ph.D degrees under his supervision. His research interests cover Electrochemistry, Green synthesis of metal, metal oxide and metal sulfide nanostructures using plant extracts, gums, polymers; novel visible-light active semiconductor nanocomposites, carbon nanomaterials and their applications towards the sensors, catalysis, bio-imaging, drug delivery systems and photocatalytic degradation of organic pollutants for safety of the environment.

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