Influence of parameters on the heterogeneous photocatalytic degradation of pesticides and phenolic contaminants in wastewater: A short review

As an alternative to the gold standard TiO2 photocatalyst, the use of zinc oxide (ZnO) as a robust candidate for wastewater treatment is widespread due to its similarity in charge carrier dynamics upon bandgap excitation and the generation of reactive oxygen species in aqueous suspensions with TiO2. However, the large bandgap of ZnO, the massive charge carrier recombination, and the photoinduced corrosion–dissolution at extreme pH conditions, together with the formation of inert Zn(OH)2 during photocatalytic reactions act as barriers for its extensive applicability. To this end, research has been intensified to improve the performance of ZnO by tailoring its surface-bulk structure and by altering its photogenerated charge transfer pathways with an intention to inhibit the surface-bulk charge carrier recombination. For the first time, the several strategies, such as tailoring the intrinsic defects, surface modification with organic compounds, doping with foreign ions, noble metal deposition, heterostructuring with other semiconductors and modification with carbon nanostructures, which have been successfully employed to improve the photoactivity and stability of ZnO are critically reviewed. Such modifications enhance the charge separation and facilitate the generation of reactive oxygenated free radicals, and also the interaction with the pollutant molecules. The synthetic route to obtain hierarchical nanostructured morphologies and study their impact on the photocatalytic performance is explained by considering the morphological influence and the defect-rich chemistry of ZnO. Finally, the crystal facet engineering of polar and non-polar facets and their relevance in photocatalysis is outlined. It is with this intention that the present review directs the further design, tailoring and tuning of the physico-chemical and optoelectronic properties of ZnO for better applications, ranging from photocatalysis to photovoltaics.

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Zinc oxide based photocatalysis: tailoring surface-bulk structure and related interfacial charge carrier dynamics for better environmental applications

Recovery, concentration and purification of phenolic compounds by adsorption: A review

Fenton processes have gained much attention in the field of wastewater treatment during recent years. In order to overcome the disadvantages of Fenton processes, research has focused more on the heterogeneous Fenton process, with highly active and stable solid catalysts. This review reports on advances in the field of heterogeneous Fenton processes in recent years, especially focusing on the various heterogeneous catalysts used. After a general introduction to the various Fenton processes, their advantages and the importance of heterogeneous Fenton processes, various catalysts used in heterogeneous Fenton processes are described in detail. These catalysts are divided into iron minerals, zero-valent iron, waste materials, iron- and iron oxide-loaded materials, and clay. The properties, stability, activity and pollutant degradation mechanism of various catalysts are also discussed in detail.

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Heterogeneous Fenton catalysts for the abatement of organic pollutants from aqueous solution: a review

Hydrogen production via photocatalytic water splitting using sunlight has enormous potential in solving the worldwide energy and environmental crisis. The key challenge in this process is to develop efficient photocatalysts which must satisfy several criteria such as high chemical and photochemical stability, effective charge separation and strong sunlight absorption. The combination of different semiconductors to create composite materials offers a promising way to achieve efficient photocatalysts because doing so can improve the charge separation, light absorption and stability of the photocatalysts. In this review article, we summarized the most recent studies on semiconductor composites for hydrogen production under visible light irradiation. After a general introduction about the photocatalysis phenomenon, typical heterojunctions of widely studied heterogeneous semiconductors, including titanium dioxide, cadmium sulfide and graphitic carbon nitride are discussed in detail.

Nanocomposite heterojunctions as sunlight-driven photocatalysts for hydrogen production from water splitting

Synthesis and characterization of nano-sized porous gamma-alumina by control precipitation method

Hydrated titania was prepared by a sol–gel method, taking tetraisopropyl orthotitanate as starting material, and then promoted with different weight percentages of sulfate by an incipient wetness impregnation method The materials were characterized by various advanced techniques such as PXRD, BET surface area, N2 adsorption–desorption measurements, FTIR, and SEM Analytical results demonstrated that TiO2 is mesoporous in nature, and sulfate modification could inhibit the phase transformation and enhance the thermal stability of TiO2 It was also found that sulfate modification could reduce the crystallite size and increase the specific surface area of the catalysts The degradation of methyl orange under solar radiation was investigated to evaluate the photocatalytic activity of these materials Effects of different parameters such as pH of the solution, amount of catalyst, additives, and kinetics were investigated At 25 wt% sulfate loading, the average percentage of degradation of methyl orange was nearly two times than that of neat TiO2 The photocatalytic degradation followed first-order kinetics

Preparation, characterization, and photocatalytic activity of sulfate-modified titania for degradation of methyl orange under visible light.

Fabrication of mesoporous CuO/ZrO2-MCM-41 nanocomposites for photocatalytic reduction of Cr(VI)

The one-dimensional (1D) mesoporous and interconnected nanoparticles (NPs) enriched composite Co3O4–CuO nanofibers (NFs) in the ratio Co:Cu = 1/4 (Co3O4–CuO NFs) composite have been synthesized by electrospinning and calcination of mixed polymeric template. Not merely the mesoporous composite Co3O4–CuO NFs but also single mesoporous Co3O4 NFs and CuO NFs have been produced for comparison. The choice of mixed polymer templates such as polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG) for electrospinning is responsible for the formation of 1D mesoporous NFs. The HR-TEM result showed evolution of interconnected nanoparticles (NPs) and creation of mesoporosity in all electrospun NFs. The quantum confinement is due to NPs within NFs and has been proved by the surface-enhanced Raman scattering (SERS) study and the UV–vis–NRI diffuse reflectance spectra (DRS). The high intense photoluminescence (PL) spectra showing blue shift of all NFs also confirmed the quantum confinement phenomena. The lowering of PL ...

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Morphological Control of Mesoporosity and Nanoparticles within Co3O4–CuO Electrospun Nanofibers: Quantum Confinement and Visible Light Photocatalysis Performance

The hybrid structure of nanoparticles (NPs) with nanosheets has the advantage of both anisotropic properties of NPs and large specific surface areas of nanosheets, which is desirable for many technological applications. In this study, MgCr2O4 spinel NPs decorated on highly porous MgO nanosheets forming MgO/MgCr2O4(x) nanocomposites were synthesized by a one pot coprecipitation method followed by a heat treatment process of the solvated wet gel of MgCr-LDH with polar solvent N,N-dimethylformamide (DMF) at 400 °C. This novel synthetic methodology generates materials consisting of porous metal oxides nanosheets adhered with spinel phase NPs due to the slow generation of gases such as H2O, CO2, and NH3 under moderate temperature during the heat treatment process. The synergistic effect of much wider band gap MgO nanosheets and narrow band gap MgCr2O4 NPs added increased stability due to the stronger bonding coordination of MgCr2O4 NPs with MgO nanosheets. The obtained MgO/MgCr2O4(x) nanocomposites possess lar...

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Amaresh C. Pradhan

Papers

Synthesis and characterization of nano-sized porous gamma-alumina by control precipitation method

Preparation, characterization, and photocatalytic activity of sulfate-modified titania for degradation of methyl orange under visible light.

Fabrication of mesoporous CuO/ZrO2-MCM-41 nanocomposites for photocatalytic reduction of Cr(VI)

Morphological Control of Mesoporosity and Nanoparticles within Co3O4–CuO Electrospun Nanofibers: Quantum Confinement and Visible Light Photocatalysis Performance

Topotactic Transformation of Solvated MgCr-LDH Nanosheets to Highly Efficient Porous MgO/MgCr2O4 Nanocomposite for Photocatalytic H2 Evolution