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Herein, the activated carbon (AC) loaded BiOBr nanoplates (AC-BiOBr) was synthesized by solvothermal method. The characterizations were done by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscope (TEM) and x-ray diffraction (XRD) to perceive the morphology, composition, inner structure, and phase of prepared samples respectively. FESEM images revealed that BiOBr is composed of variable sizes of microspheres, constructed by many interlaced nanoplates. Thermogravimetric analysis (TGA) confirms the stability and purity of samples. The as-prepared activated loaded composites were evaluated via the removal of Rhodamine B (RhB) dye under visible light. The AC-BiOBr nanocomposites exhibited superior adsorption capacity, consequently improved photocatalytic efficiency. The better degradation efficiency of the AC-BiOBr nanocomposite is attributed to higher the adsorption capacity of dye on its surface, and enhanced charge separation through adsorbed O2 in AC. Kinetic parameters like pseudo-first-order and pseudo-second-order were determined. The adsorption of RhB dye on AC-BiOBr follows the second-order kinetic model. Langmuir adsorption isotherm is the most fitted isotherm for adsorption of RhB dye on AC-BiOBr. The composite surface provides the more adsorption surface sites for photodegradation, in addition, could restrict the toxic intermediates to release in air or solution phase.

An efficient synthesis of Hantzsch 1,4-dihydropyridines via a one-pot three-component reaction of ethyl acetoacetate, substituted aldehydes and ammonium acetate in the presence of ZnO@SnO2 mixed metal oxide nanoparticles under solvent-free conditions has been reported. Compare to the reported reactions, this method shows attractive aspects such as cleaner reaction profile, shorter reaction times, minimum catalyst loading and high yields. Isolated catalysts were reused for new reactions without considerable loss of their catalytic activity.

Graphene and its derivatives have received extensive attention of the scientific community to resolve energy renovation and environmental pollution-related issues. Graphene and its derivatives have extraordinary properties such as a unique atom-thick, two-dimensional structure; high surface area; exceptional conductivity; high electron mobility; anticorrosion ability; photosensitivity; and excellent chemical stability, which provides a route for an efficient and effective photocatalyst. Also, graphene-based composites offer enhanced adsorption, effective photoinduced charge separation, and an extended light-absorption range. Accordingly, it emerged as a versatile photocatalyst for the degradation of a variety of organic pollutants, H2 production via water-splitting, and CO2 reduction. Different methods such as solvothermal, hydrothermal, wet impregnation, combustion method, electrochemical techniques, photochemical reactions, and physical deposition have been used to fabricate potential graphene-based photocatalysts. Different derivatives of graphene, including graphene oxide and reduced graphene oxide, have been explored to prepare graphene-based photocatalysts. This chapter summarizes the recent developments in graphene-based photocatalysts, specifically different approaches to improve the photocatalytic efficiency of graphene and its derivative-based materials for organic pollutant degradation, H2 production, and CO2 reduction.

“Water” is an essential natural resource for every organism in the universe. One of the major global challenges in the 21st century is to overcome water pollution, and attention should be given for water purity. Membrane-based technologies (polymer) have added value in water purification as an advanced separation technique; however, there are stability issues limiting their utilization. Therefore, the best material with efficient performance and unique properties (for the purification of water) is still in high demand. In this regard, nanotechnology has shown potential applications in environmental sustainability. Carbon nanotubes (CNT), for example, is one of the best outstanding candidates used in the era of materials science because of their excellent physicochemical properties. Nowadays, utilization of CNT nanocomposite (carbon-based nanocomposite) membrane for water purification has been of keen interest due to its one-dimensional nanochannel structure that leads to high water permeability, high mechanical strength, excellent absorption ability, greater thermal stability, etc. This chapter particularly presents the potential and advanced applications of carbon-based nanocomposite membranes for water purification. It summarizes the flexibility in synthesis, characterization, and new fabrication methods/techniques for the development of high-performance carbon-based nanocomposite membranes. The current status with real applications and challenges of carbon-based nanocomposite membrane generally in water purification has also been discussed.

A simple hydrothermal method is adopted to prepare ternary Mn doped ZnO nanoparticles uniformly grafted on reduced graphene oxide (RGO) sheets. The effect of Mn doping on ZnO/RGO nanocomposite has been investigated using different characterization techniques. Field emission scanning electron microscope (FESEM) images clearly show the uniform distribution of nanoparticles on RGO sheets. The doping of Mn in ZnO/RGO composites have been confirmed by X-ray photoelectron spectroscopy (XPS). Photocatalytic activities of as-prepared samples were examined by the degradation of Rhodamine B (RhB) and Congo red (CR) under sun light. The prepared ternary heterojunction photocatalyst exhibit the excellent photocatalytic activity for degradation of RhB (degradation rate nearly 99% within 140 min) and CR (degradation rate nearly 100% within 160 min) under sunlight irradiation which is higher than that of binary ZnO/RGO heterojunction. The improved photocatalytic performance of the ternary nanocomposite can be ascribed to extend solar light absorption, enhanced adsorption of the composite catalyst surface and efficient charge separation of photo-induced electrons.

Rare-earth cerium (Ce)-doped zinc oxide (ZnO) spherical nanoparticles were synthesized by using the co-precipitation method. The doped materials were characterized by means of the X-ray diffraction, Williamson-Hall Plot, and field emission scanning electron microscopy analyses. The prepared nanoparticles exhibit a hexagonal wurtzite structure as observed from the XRD measurements. Energy dispersive X-ray spectroscopy data confirmed the purity of the prepared samples. The photocatalytic activity of the rare-earth Ce-doped ZnO spherical nanoparticles was investigated through the degradation of methylene blue (MB) and p-nitrophenol (PNP) solution under UV light radiation. Among the different amounts of dopant, 5 mole% Ce-doped ZnO nanoparticles showed the highest degradation with UV light radiation for both MB dye and PNP solution. The particle size, morphology, and separation of the photo-induced electron–hole pair are the main factors that influence photocatalytic activity. The probable mechanisms of photocatalytic degradation and mineralization of MB and PNP are also explained by liquid chromatography–mass spectrometry analysis.

Mg doped ZnO nanoparticles decorated on graphene oxide (GO) sheets were synthesized by a wet impregnation method. The effect of Mg doping on ZnO and ZnO-GO composite has been evaluated by using x-ray diffraction (XRD), Williamson-Hall Plot (W H Plot), field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy (EDX). The physical parameters of as-prepared samples were estimated by XRD data. FESEM and HR-TEM images showed the uniform distribution of nanoparticles on GO crumpled paper like sheet. Solar light photocatalytic activities of samples were evaluated spectrophotometrically by the degradation of p-nitrophenol (PNP) and indigo carmine (IC) solution. Mg ZnO decorated on GO sheets exhibit excellent catalytic efficiency compared to all other prepared samples under identical conditions, degrading PNP and IC nearly 99% within 60 min under sunlight. The effective degradation by Mg ZnO decorated on GO sheet would be due to extended solar light absorption, enhanced adsorptivity on the composite catalyst surface and efficient charge separation of photo-induced electrons. Finally, plausible mechanism was suggested with the help of scavengers study.

Formulation of visible light responsive photocatalyst with excellent adsorption and great electron-holes reduction in semiconductor-based catalyst is always a major concern for scientific community. In this report a visible light responsive ZnS nanospheres immobilized on activated carbon (AC-ZnS) photocatalyst was prepared by mixed solvothermal method. The crystallographic properties, morphologies, thermal stability, adsorption properties and photocatalytic performance of prepared samples were studied by several methods. The results of XRD were used to analyze various physical parameters of prepared catalyst. The nanocomposite photocatalysts were used to analyze adsorption and photocatalytic study on Congo red dye, a model organic pollutant. The adsorption followed by photocatalysis with as-prepared catalyst offers an excellent performance for the abatement of Congo red. Moreover, radical scavengers study revealed that hydroxyl radicals are the main contributors for the photocatalytic degradation of Congo red with AC-ZnS nanocomposite. Eventually, through various characterizations and synergy of effective adsorption and enhanced photocatalytic degradation, AC-ZnS nanocomposite proved to be an economical, environmentally friendly and highly efficient material for photocatalytic processes.

A highly efficient, green protocol has been developed for the synthesis of various structurally diverse 2,2′-arylmethylene bis(3-hydroxy-5,5-dimethyl-2-cyclohexene-1-one) and 2-substituted-1H-benzimidazole derivatives. The reaction was performed in water under ultrasound irradiation, using BiOCl nanoparticles as a catalyst. The nanocatalyst was found to be reusable for seven subsequent reactions without much loss in activity. Simple methodology with short reaction times and mild reaction conditions with easy work-up procedure are the salient features of this method.

Reduced graphene oxide (RGO) sheets decorated by ZnO nanoparticles were synthesized using wet impregnation method. The composite material was characterized by means of X-ray diffraction (XRD), Williamson-Hall Plot (W-H Plot) and Scanning Electron Microscope (SEM) analysis. The XRD pattern revealed orderly hexagonal (wurtzite) structure of the ZnO nanoparticles. Surface morphology of ZnO, RGO and RGO-ZnO was investigated using SEM analysis. SEM images indicated the uniform distribution of ZnO onto the RGO surface. The photocatalytic activity of nanocomposite was demonstrated by determining the degradation of methylene blue dye. The degradation of dye took place due to efficient electron-hole recombination of photo-induced electrons. Finally, plausible mechanism was explained with the help of scavengers. Overall, wet impregnation method was found efficient to produce RGO with uniform ZnO loading. The prepared RGO-ZnO composite can efficiently degrade the dye under UV radiation.

Herein, we fabricated activated carbon (AC) immobilized WO3 nanocuboids (AC-WO3) as an efficient and green photocatalyst via simple hydrothermal method. AC-WO3 shows great potential for the removal of stable rhodamine B (RhB) dye in aqueous solution under visible light. The large surface area of the AC-WO3 nanocomposites brought numerous active sites for the adsorption, consequently, for photodegradation of RhB dye. The characterization results established that the prepared material has crystalline orthorhombic structure, nanosized cuboids shape like morphology, visible light responsive nature, thermo stability and smaller particle size with high specific surface area. Adsorption isotherm studies revealed homogeneous surface adsorption with Langmuir adsorption isotherm. Study on adsorption kinetics confirms that adsorption of dye on AC-WO3 follows the second order kinetic model. AC-WO3 nanocomposites exhibit enhancing synergistic effect of adsorption and photodegradation ability for removing RhB in aqueous solution.

Herein, we prepared AC (activated carbon) loaded CdS nanoflowers for the removal of stable dye. Morphological, crystallographic, thermal and optical properties of activated carbon loaded CdS nanoflowers (AC-CdS) were comprehensively studied using multiple characterizations. The prepared samples were examined for the removal of rhodamine B (RhB) under visible light. The AC-CdS photocatalyst exhibit flower-like morphology and flowers were composed of several assembled nanoplates. The AC-CdS nanoflowers allows the maximum adsorption of dye on catalyst surface and assist efficient charge separation, which ultimately enhanced its photocatalytic performance. The enhanced photocatalytic performance is owing to synergistic effect of adsorption and photocatalysis. Further, the AC in AC-CdS nanoflowers effectively adsorbed the intermediates/toxic materials formed during photocatalysis. Therefore, the AC-CdS flower-like nanocomposites would be an economical, efficient and greener environment-friendly photocatalyst. The kinetic study shows that the adsorption of RhB on AC-CdS follows the pseudo-second-order kinetic model.

Herein, we report a raspberry-shaped reduced graphene oxide labelled Fe-CeO2 ternary photocatalyst synthesized via simple hydrothermal method. In order to evaluate structural, morphological, elemental composition and optical properties, resultant photocatalysts were characterized by x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM), energy dispersive x-ray analysis (EDX), photoluminescence (PL) and UV–visible spectroscopy respectively. The photocatalytic efficiency of as-prepared ternary catalyst was investigated by the degradation of congo red dye (CR) in aqueous medium under UV light. The ternary Fe-CeO2/RGO nanocomposite show outstanding photocatalytic degradation performance. The co-ordination and synergistic effect between reduced graphene oxide sheets and redox system of the cerium (Ce4+/ Ce3+) along with iron (Fe3+/ Fe2+) are accountable for the excellent photocatalytic performance of Fe-CeO2/RGO nanocomposite. The reduced graphene oxide sheets and redox systems acts as a trapping sites for photogenerated electrons and thereby significantly reduced the recombination of charge carriers. Moreover, a good reusability and stability suggest that ternary material has a great ability in removal of organic pollutants. Further, this report may offer a new strategy to fabricate and design a material for energy and environmental remediation.

Carbon (C) doped ZnO rod like nanoparticles were prepared by simple co-precipitation method. The effect of C doping on ZnO has been evaluated by using XRD, Williamson-Hall Plot, FESEM and EDX data. UV light assisted photocatalytic activities of prepared samples were evaluated spectrophotometrically by the degradation of methylene blue (MB). C doped ZnO shows excellent catalytic efficiency compared to pure ZnO, degrading MB completely within 100 min under UV light. Photocatalysis follows the first order kinetics law and the calculated apparent reaction kinetics rate constant suggest the better activity of C-ZnO.

The nanoparticles of Pure and doped Ti1-xFexO were synthesized by modified co-precipitation method successfully with nominal composite of x=0.0, 0.01, 0.03 and 0.05 at room temperature. The precursors were further calcined at 500°C for 6hrs in muffle furnace which results in the formation of different TiO2 phase compositions. The structural analysis carried out by XRD (Bruker D8 Cu-Kα1). X-ray peak broadening analysis was used to evaluate the crystalline sizes, the lattice parameters, atomic packing fraction, c/a ratio, X-ray density and Volume of unit cell. The Williamson Hall analysis is used to find grain size and Strain of prepared TiO2 nano particles. Crystalline TiO2 with a Tetragonal Anatase phase is confirmed by XRD results. The grain size of pure and Fe doped samples were found in the range of 10nm to 18nm. All the physical parameters of anatase tetragonal TiO2 nanoparticles were calculated more precisely using modified W-H plot a uniform deformation model (UDM). The results calculated from both the techniques were approximately similar.

Nanoparticles of Zn1-xCuxO system with nominal compositions x = 0.0, 0.01, 0.02 and 0.03 were prepared by co-precipitation method at room temperature. Structural, morphological, optical and chemical species of grown crystals were investigated by X-ray diffraction (XRD) technique, Scanning Electron Microscopy (SEM), UV-visible and FTIR spectroscopy, respectively. XRD analysis confirms that all samples have hexagonal structure with no impurity phases which suggest that Cu ion successfully incorporated into the regular ZnO crystal structure. The lattice parameters, volume of unit cell, X-ray density, atomic packing fraction, c/a ratio, and grain size were calculated from XRD pattern of pure and Cu doped ZnO samples and it was found that the grain size was in the range of 23 nm to 29 nm. The strain in pure and Cu doped ZnO samples was calculated by W-H analysis. Optical properties of Zn1-xCuxO samples were studied by using UV-vis spectrophotometer. Optical absorption spectra show that the band gap decreases with increasing Cu contents. The functional group and chemical interactions of Zn1-xCuxO samples were also determined at various peaks using FTIR data and observed that the functional groups corresponding to the Zn-O bands in the samples. The photocatalytic activities of the samples were investigated by oxidation of methylene blue under UV light illumination in batch reactor. The scavenger study was carried out to find out main reactive species responsible for the degradation of dyes.