Comparative Studies on Structural, Optical, and Textural Properties of Combustion Derived ZnO Prepared Using Various Fuels and Their Photocatalytic Activity

Preparation of nanocomposite based on chitosan-PDCOEMA containing biosynthesized ZnO: Biological and thermal characterization

In this study, poly(2-(3,5-dichloroanilino)-2-oxoethyl 2-methylprop-2-enoate) (PDCOEMA), a new synthetic polymer based on methacrylate, was synthesized and characterized. The blend of PDCOEMA with chitosan (CS) was prepared by the hydrothermal method and the DSC technique confirmed its formation. It was observed that PDCOEMA increased the thermal stability and glass transition temperature (Tg) of CS. The Tg value of the PDCOEMA-CS blend was increased at about 7 °C with the highest ZnO NPs contribution rate. PDCOEMA-CS/ZnO nanocomposites were prepared by adding ZnO NPs produced by biosynthesis at different weight ratios to the PDCOEMA-CS blend by hydrothermal method. When the thermal stability of nanocomposites determined by TGA was examined, it was observed that it increased significantly compared to CS. While the initial decomposition temperature of CS was 270 °C, this value increased to 293 °C after blending with DCOEMA, and to 317 °C with the addition of 7 % ZnO NPs. Antimicrobial, anticancer, cytotoxic, antioxidant, and wound healing properties of PDCOEMA, CS, PDCOEMA-CS blend, and nanocomposites were determined. According to the obtained results, it was observed that nanocomposites containing 5 % and 7 % ZnO NPs showed good anticancer activity against A549 cells at a dose of 10 μg/mL. The results show that the produced nanocomposites can contribute to developing CS-based materials.

Solution combustion synthesis: the relevant metrics for producing advanced and nanostructured photocatalysts

The current developments and progress in energy and environment-related areas pay special attention to the fabrication of advanced nanomaterials via green and sustainable paths to accomplish chemical circularity. The design and preparation methods of photocatalysts play a prime role in determining the structural, surface characteristics and optoelectronic properties of the final products. The solution combustion synthesis (SCS) technique is a relatively novel, cost-effective, and efficient method for the bulk production of nanostructured materials. SCS-fabricated metal oxides are of great technological importance in photocatalytic, environmental and energy applications. To date, the SCS route has been employed to produce a large variety of solid materials such as metals, sulfides, carbides, nitrides and single or complex metal oxides. This review intends to provide a holistic perspective of the different steps involved in the chemistry of SCS of advanced photocatalysts, and pursues several SCS metrics that influence their photocatalytic performances to establish a feasible approach to design advanced photocatalysts. The study highlights the fundamentals of SCS and the importance of various combustion parameters in the characteristics of the fabricated photocatalysts. Consequently, this work deals with the design of a concise framework to link the fine adjustment of SCS parameters for the development of efficient metal oxide photocatalysts for energy and environmental applications.

Review on optofluidic microreactors for photocatalysis

Four interrelated issues have been arising with the development of modern industry, namely environmental pollution, the energy crisis, the greenhouse effect and the global food crisis. Photocatalysis is one of the most promising methods to solve them in the future. To promote high photocatalytic reaction efficiency and utilize solar energy to its fullest, a well-designed photoreactor is vital. Photocatalytic optofluidic microreactors, a promising technology that brings the merits of microfluidics to photocatalysis, offer the advantages of a large surface-to-volume ratio, a short molecular diffusion length and high reaction efficiency, providing a potential method for mitigating the aforementioned crises in the future. Although various photocatalytic optofluidic microreactors have been reported, a comprehensive review of microreactors applied to these four fields is still lacking. In this paper, we review the typical design and development of photocatalytic microreactors in the fields of water purification, water splitting, CO2 fixation and coenzyme regeneration in the past few years. As the most promising tool for solar energy utilization, we believe that the increasing innovation of photocatalytic optofluidic microreactors will drive rapid development of related fields in the future.

Strategies to Enhance ZnO Photocatalyst's Performance for Water Treatment: A Comprehensive Review

Despite the photocatalytic organic pollutant degradation using ZnO started in 1910-1911, many challenges are still ahead, and several critical issues have to be addressed. Large band gap, and short life-time of photogenerated electrons and holes are critical issues negatively affect the photocatalytic activity of ZnO. Various approaches have been introduced to overcome these issues including intrinsic doping, extrinsic doping, and heterostructure. This review introduces unique and deep insights into tuning of the photocatalytic activity of ZnO. It starts by description of how to tune the photocatalytic activity of pristine ZnO through tuning its morphology, surface area, exposed face, and intrinsic defects. Afterward, the review explains how the Z-scheme approach succeed to address the redox weakened issue of heterojunction approach. In general, this review provides a clear image that helps the researcher to tune the photocatalytic activity of pristine ZnO and its heterostructure.

Microflow synthesis and enhanced photocatalytic dye degradation performance of antibacterial Bi2O3 nanoparticles

Microreactors can play a crucial role in synthesis and rapid testing of various nanocatalyst to be used in addressing the issue of environmental contamination. We have reported the rapid fabrication of polydimethylsiloxane (PDMS) and poly(methyl methacrylate) (PMMA)-based microreactor for the flow synthesis and enhanced inline photocatalysis of bismuth oxide (Bi₂O₃) nanoparticles. A T-shaped microreactor with uniform circular cross-sectional channel having inner diameter of 450 μm was utilized for synthesizing Bi₂O₃ nanoparticles with narrow size distribution. Further, photocatalytic dye degradation efficiency for methyl orange (MO) was recorded by coating these Bi₂O₃ nanoparticles within the inner walls of PMMA-based serpentine microreactors under visible light. The enhanced dye degradation efficiency of as high as 96% within just 15 min of irradiation is reported. A comparative analysis has also been done for both conventional as well as the in-channel photocatalysis highlighting the advantages of microreactor based photocatalysis over the conventional method. Bi₂O₃ nanoparticles also showed excellent stability even after three cycles indicating reusability of coated microreactors in photocatalysis. The small concentration of as synthesized Bi₂O₃ nanoparticles also demonstrated high efficacy for the inhibition of Escherichia coli bacterial pathogens.

Enhancing photocatalytic degradation of quinoline by ZnO:TiO2 mixed oxide: Optimization of operating parameters and mechanistic study

This study focuses on the photocatalytic degradation of quinoline, a recalcitrant heterocyclic nitrogenous aromatic organic compound, using the mixed oxide ZnO-TiO₂ photo-catalyst. Photo-catalysts were synthesized by the solid-state reaction method at different calcination temperatures of 400 °C, 600 °C, and 800 °C. Different analytical methods, including Field emission scanning electron microscope, Brunauer-Emmett-Teller surface area, X-ray diffraction, UV-vis diffuse reflectance spectroscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy analysis were used for the catalyst characterization. The highest pore surface area of 57.9 m²g^-1 was obtained for the photo-catalyst calcined at 400 °C. The effects of calcination temperature, solution pH, initial concentration, catalyst dose as well as irradiation time were studied. At the optimum condition, i.e., calcination temperature of 400 °C, pH ≈8 and catalyst dose of 2.5 gL^-1, maximum quinoline degradation and total organic carbon (TOC) removal efficiency of ≈92% and ≈78% were obtained after 240 min for initial quinoline amount of 50 mgL^-1. The 1^st, 2^nd, and n^th-order kinetic models were applied to analyze the quinoline degradation rate. The photocatalytic mechanism was studied by drawing energy level diagram with the help of the band-gap structures of the ZnO and TiO₂, potential of the free radicals like OH and O₂ and HOMO-LUMO energy gap of the quinoline molecule. The proposed pathways of quinoline mineralization were suggested on the basis of the identified intermediates by the gas chromatograph-mass spectrometer analysis and scavenger study.

Fabrication of Ag-doped ZnO by mechanochemical combustion method and their application into photocatalytic Famotidine degradation

Ag/ZnO nanocomposites are successfully synthesized at different Ag contents through simple, effective, high yield and low-cost mechanochemical combustion technique, with the addition of silver acetate to zinc acetate and oxalic acid mixture. The synthesized materials are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron spectroscopy (SEM), BET surface area analysis, UV - visible diffuse reflectance spectroscopy (UV - DRS) and photoluminescence spectroscopy (PL). It is shown that the prepared nanocomposites are composed of metallic Ag⁰ and wurtzite ZnO. The photocatalytic performance of different composites is evaluated by the degradation of Famotidine (FMT) under UV irradiation. The results indicate it that the maximum photodegradation rate is obtained with 6 wt% metallic Ag-decorated ZnO, and it is 2.1 times better than that obtained with pure ZnO. The photocatalytic degradation of FMT with Ag/ZnO is affected by various parameters such as calcination temperature and time, doping concentrations and reusability. The Ag/ZnO demonstrates higher activity due to the reduction of electron - hole recombination and Ag⁰ metal catalyst. The possible photocatalytic degradation mechanism of FMT with Ag/ZnO is estimated from the scavenger test.

Studies of Effects of Calcination Temperature on the Crystallinity and Optical Properties of Ag-Doped ZnO Nanocomposites

Ag-doped ZnO nanocomposites are successfully synthesized at different calcination temperatures and times through a simple, effective, high-yield and low-cost mechanochemical combustion technique. Effects of calcination temperature on the crystallinity and optical properties of Ag/ZnO nanocomposites have been studied by X-ray diffraction (XRD), UV−visible diffuse reflectance spectroscopy (UV-DRS), photoluminescence spectroscopy (PL) and X-ray photoelectron spectroscopy (XPS). The XRD patterns of the synthesized Ag/ZnO exhibit a well-crystalline wurtzite ZnO crystal structure. The grain size of Ag/ZnO nanocomposites is found to be 19 and 46 nm at calcination temperatures of 400 °C and 700 °C, respectively. The maximum absorption in the UV region is obtained for Ag/ZnO nanocomposites synthesized at a calcination temperature of 500 °C for 3 h. The peak position of blue emissions is almost the same for the nanocomposites obtained at 300–700 °C calcination temperatures. The usual band edge emission in the UV is not obtained at 330 nm excitation. Band edge and blue band emissions are observed for the use of low excitation energy at 335–345 nm.

Synthesis and application of green mixed-metal oxide nano-composite materials from solid waste for dye degradation

Present study demonstrates reutilization of electrochemical (EC) sludge as a potential low-cost green catalyst for dye degradation. Hexagonal Fe2O3 type phase with trevorite (NiFe2O4)-type cubic phase nanocomposite material (NCM) was synthesized from solid waste sludge generated during EC treatment of textile industry wastewater with stainless steel electrode. For NCM synthesis, sludge was heated at different temperatures under controlled condition. Various synthesized NCMs were characterized by powder X-ray diffraction (PXD), energy dispersive X-ray (EDX) spectroscopy and X-ray photoelectron spectroscopy (XPS) analysis. The synthesized NCMs were found to contain iron, chromium, nickel and oxygen in the form of α-Fe2O3 (metal: oxygen = 40:60), (Fe,Cr,Ni)2O3 and trevorite NiFe2O4, (Ni,Fe,Cr) (Fe,Cr,Ni)2O4 (metal: oxygen = 43:57). Field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), pore size distribution, and atomic force microscope (AFM) analysis showed distribution of grains of different shapes and sizes. Catalytic activity of NCM was studied by the methylene red dye degradation by using the catalytic wet peroxidation process. Zeta potential study was performed under different pH so as to determine the performance of the NCMs during dye degradation.

Solution Combustion Synthesis of Nanoscale Materials

Solution combustion is an exciting phenomenon, which involves propagation of self-sustained exothermic reactions along an aqueous or sol-gel media. This process allows for the synthesis of a variety of nanoscale materials, including oxides, metals, alloys, and sulfides. This Review focuses on the analysis of new approaches and results in the field of solution combustion synthesis (SCS) obtained during recent years. Thermodynamics and kinetics of reactive solutions used in different chemical routes are considered, and the role of process parameters is discussed, emphasizing the chemical mechanisms that are responsible for rapid self-sustained combustion reactions. The basic principles for controlling the composition, structure, and nanostructure of SCS products, and routes to regulate the size and morphology of the nanoscale materials are also reviewed. Recently developed systems that lead to the formation of novel materials and unique structures (e.g., thin films and two-dimensional crystals) with unusual properties are outlined. To demonstrate the versatility of the approach, several application categories of SCS produced materials, such as for energy conversion and storage, optical devices, catalysts, and various important nanoceramics (e.g., bio-, electro-, magnetic), are discussed.

Visible light assisted improved photocatalytic activity of combustion synthesized spongy-ZnO towards dye degradation and bacterial inactivation

Citric acid combusted spongy-ZnO nanopowders exhibit high catalytic activity for dye degradation and bacterial inactivation.

Microfluidic-based photocatalytic microreactor for environmental application: a review of fabrication substrates and techniques, and operating parameters

This article gives an overview of photocatalytic microreactors with an application in environmental science, in particular, the degradation of different toxic dyes within microchannels.

Effect of fuel content on luminescence and antibacterial properties of zinc oxide nanocrystalline powders synthesized by the combustion method

Nanoscale ZnO powders were synthesized via the combustion method using zinc nitrate hexahydrate as the source (oxidant) material and urea, and glycine or citric acid monohydrate as fuels.

Defect states and morphological evolution in mechanically processed ZnO + xC nanosystems as studied by EPR and photoluminescence spectroscopy

Evolution of the EPR and photoluminescence spectra of various active states in mixtures of ZnO + xC nanoparticles was observed during prolonged high-energy mechanical processing.

Highly efficient WO3–ZnO mixed oxides for photocatalysis

Monoclinic nanocuboid WO₃ enhanced the photocatalyst efficiency of quasi nanobelt zinc oxide for dye degradation in the presence of visible light radiation.

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

Surface-bulk modification of zinc oxide for efficient photocatalysis.

Low-temperature fabrication of high performance indium oxide thin film transistors

In this study, indium oxide (In₂O₃) thin-film transistors (TFTs) were fabricated by a fully-solution process at low temperature.

Synthesis of different crystallographic Al2O3 nanomaterials from solid waste for application in dye degradation

Recycling of sludge generated during electrochemical treatment to synthesize alumina nanomaterials with different crystallographic orientations.

Synthesis and photocatalytic performance of quasi-fibrous ZnO

The combustion of oxidizer zinc nitrate and fuel oxalic acid results in quasi-fibrous zinc oxide for enhanced photocatalysis under UV and visible light.