Flame spray pyrolysis synthesized ZnO/CeO 2 nanocomposites for enhanced CO 2 photocatalytic reduction under UV–Vis light irradiation

Hydrophobic Porphyrin Titanium-Based MOFs for Visible-Light-Driven CO2 Reduction to Formate

Three hydrophobic porphyrin titanium-based metal-organic frameworks (MOFs) (HPA/DGIST-1, DPA/DGIST-1, and OPA/DGIST-1) were synthesized through a postsynthetic coordination reaction by using alkylphosphonic acid of different lengths (HPA, hexylphosphonic acid; DPA, dodecylphosphonic acid; OPA, octadecylphosphonic acid). Compared with the hydrophilic DGIST-1, modified DGIST-1 exhibits excellent hydrophobicity and presents good stability in humid atmospheres. Due to the introduction of porphyrin ligands, HPA/DGIST-1, DPA/DGIST-1, and OPA/DGIST-1 showed good visible-light absorption (380-700 nm) and sensitive photogenerated charge responses. When acted as catalysts, these hydrophobic Ti-MOFs can selectively reduce CO2 to HCOO- under visible-light irradiation with average reaction rates of 150.9, 178.5, and 228.3 μmol·h-1·g-1, where these values are 1.3-2.0 times higher than the system mediated by the initial porphyrin Ti-MOF catalyst. 13C NMR spectroscopy demonstrates that the catalytic product HCOO- anion originates from the reactant CO2. The photocatalytic experiments, electron paramagnetic resonance, and photoluminescence spectra tests showed that porphyrin ligands and Ti-O units can act as catalytic activity centers to realize the conversion of CO2 to HCOO-. This work demonstrated that the combination of porphyrin titanium-based MOF and alkyl hydrophobic groups is an effective way to enhance the stability of titanium-based MOFs and maintain their high photocatalytic performance.

Research Progress of Copper-Based Bimetallic Electrocatalytic Reduction of CO2

Fossil fuels are still the main source of energy in today’s society, so emissions of CO2 are inevitable, but when the CO2 level in the atmosphere is too high, many environmental problems will arise, such as the greenhouse effect, among others. Electrocatalytic reduction of CO2 is one of the most important methods that one can use to reduce the amount of CO2 in the atmosphere. This paper reviews bimetallic catalysts prepared on the basis of copper materials, such as Ag, Au, Zn and Ni. The effects of different ratios of metal atoms in the bimetallic catalysts on the selectivity of CO2RR were investigated and the effects of bimetallic catalysts on the CO2RR of different ligands were also analysed. Finally, this paper points out that the real reaction of CO2RR still needs to be studied and analysed, and the effect of the specific reaction environment on selectivity has not been thoroughly studied. This article also describes some of the problems encountered so far.

Facile Synthesis of ZnO-CeO2 Heterojunction by Mixture Design and Its Application in Triclosan Degradation: Effect of Urea

In this study, simplex centroid mixture design was employed to determine the effect of urea on ZnO-CeO. The heterojunction materials were synthesized using a solid-state combustion method, and the physicochemical properties were evaluated using X-ray diffraction, nitrogen adsorption/desorption, and UV–Vis spectroscopy. Photocatalytic activity was determined by a triclosan degradation reaction under UV irradiation. According to the results, the crystal size of zinc oxide decreases in the presence of urea, whereas a reverse effect was observed for cerium oxide. A similar trend was observed for ternary samples, i.e., the higher the proportion of urea, the larger the crystallite cerium size. In brief, urea facilitated the co-existence of crystallites of CeO and ZnO. On the other hand, UV spectra indicate that urea shifts the absorption edge to a longer wavelength. Studies of the photocatalytic activity of TCS degradation show that the increase in the proportion of urea favorably influenced the percentage of mineralization.

Green-synthesized CeO2 nanoparticles for photocatalytic, antimicrobial, antioxidant and cytotoxicity activities

Cerium oxide nanoparticles (CeO2 NPs) are a sought-after material in numerous fields due to their potential applications such as in catalysis, cancer therapy, photocatalytic degradation of pollutants, sensors, polishing agents. Green synthesis usually involves the production of CeO2 assisted by organic extracts obtained from plants, leaves, flowers, bacteria, algae, food, fruits, etc. The phytochemicals present in the organic extracts adhere to the NPs and act as reducing and/or oxidizing agents and capping agents to stabilize the NPs, modify the particle size, morphology and band gap energy of the as-synthesized materials, which would be advantageous for numerous applications. This review focuses on the green extract-mediated synthesis of CeO2 NPs and discusses the effects on CeO2 NPs of various synthesis methods that have been reported. Several photocatalytic, antimicrobial, antioxidant and cytotoxicity applications have been evaluated, compared and discussed. Future prospects are also suggested.

Vapor-phase production of nanomaterials

The synthesis of nanomaterials, with characteristic dimensions of 1 to 100 nm, is a key component of nanotechnology. Vapor-phase synthesis of nanomaterials has numerous advantages such as high product purity, high-throughput continuous operation, and scalability that have made it the dominant approach for the commercial synthesis of nanomaterials. At the same time, this class of methods has great potential for expanded use in research and development. Here, we present a broad review of progress in vapor-phase nanomaterial synthesis. We describe physically-based vapor-phase synthesis methods including inert gas condensation, spark discharge generation, and pulsed laser ablation; plasma processing methods including thermal- and non-thermal plasma processing; and chemically-based vapor-phase synthesis methods including chemical vapor condensation, flame-based aerosol synthesis, spray pyrolysis, and laser pyrolysis. In addition, we summarize the nanomaterials produced by each method, along with representative applications, and describe the synthesis of the most important materials produced by each method in greater detail.

Eco-friendly synthesis of chromeno[4,3-b]chromenes with a new photosensitized WO3/ZnO@NH2-EY nanocatalyst

A new heterogeneous photoredox nanocatalyst WO₃/ZnO@NH₂-EY (EY: eosin Y) was fabricated and characterized employing some instrumental techniques such as XRD, FT-IR, ICP, TGA, and SEM. The photocatalytic efficiency of the prepared material was investigated in the preparation of various chromeno[4,3-b]chromenes via a simple and practical method. The chromene derivatives were prepared through the condensation of aromatic aldehydes, dimedone, and coumarin under an open-air atmosphere in the presence of a green LED under solventless conditions. The significant advantages of this new method include low reaction time, easy work-up, cost-effective, wide substrate scope, excellent yield, and complete atom economy of the final products. Moreover, the prepared photocatalyst could be frequently recovered up to four times with only a little decrease in the catalytic activity. Furthermore, the progress of the condensation reaction is demonstrated to occur via a radical mechanism, which shows that reactive species such as ˙O₂⁻ and OH˙ together with h⁺ would be involved in the photocatalytic process. Stability and reusability studies also warranty good reproducibility of the nanocatalyst for at least 4 runs. Eventually, a hot filtration test ensured that the nanohybrid catalyst is stable in the reaction medium and its catalytic activity originates from the whole undecomposed conjugated composite.

WO₃/ZnO@NH₂-EY is disclosed in the preparation of chromenes under air in the presence of a green LED. ˙O₂⁻, OH˙, and h⁺ are proposed as reactive species and hot filtration test assured stability and reusability of the nanocatalyst.

Hypercrosslinked Polymers as a Photocatalytic Platform for Visible-Light-Driven CO2 Photoreduction Using H2 O

The design of robust, high-performance photocatalysts is key for the success of solar fuel production by CO2 conversion. In this study, hypercrosslinked polymer (HCP) photocatalysts have been developed for the selective reduction of CO2 to CO, combining excellent CO2 sorption capacities, good general stabilities, and low production costs. HCPs are active photocatalysts in the visible light range, significantly outperforming the benchmark material, TiO2 P25, using only sacrificial H2 O. It is hypothesized that superior H2 O adsorption capacities facilitate access to photoactive sites, improving photocatalytic conversion rates when compared to sacrificial H2 . These polymers are an intriguing set of organic photocatalysts, displaying no long-range order or extended π-conjugation. The as-synthesized networks are the sole photocatalytic component, requiring no added cocatalyst doping or photosensitizer, representing a highly versatile and exciting platform for solar-energy conversion.

Synthesis, Crystallography, Microstructure, Crystal Defects, Optical and Optoelectronic Properties of ZnO:CeO2 Mixed Oxide Thin Films

We report the synthesis and characterization of pure ZnO, pure CeO2, and ZnO:CeO2 mixed oxide thin films dip-coated on glass substrates using a sol-gel technique. The structural properties of as-prepared thin film are investigated using the XRD technique. In particular, pure ZnO thin film is found to exhibit a hexagonal structure, while pure CeO2 thin film is found to exhibit a fluorite cubic structure. The diffraction patterns also show the formation of mixed oxide materials containing well-dispersed phases of semi-crystalline nature from both constituent oxides. Furthermore, optical properties of thin films are investigated by performing UV–Vis spectrophotometer measurements. In the visible region, transmittance of all investigated thin films attains values as high as 85%. Moreover, refractive index of pure ZnO film was found to exhibit values ranging between 1.57 and 1.85 while for CeO2 thin film, it exhibits values ranging between 1.73 and 2.25 as the wavelength of incident light decreases from 700 nm to 400 nm. Remarkably, refractive index of ZnO:CeO2 mixed oxide-thin films are tuned by controlling the concentration of CeO2 properly. Mixed oxide-thin films of controllable refractive indices constitute an important class of smart functional materials. We have also investigated the optoelectronic and dispersion properties of ZnO:CeO2 mixed oxide-thin films by employing well-established classical models. The melodramatic boost of optical and optoelectronic properties of ZnO:CeO2 mixed oxide thin films establish a strong ground to modify these properties in a skillful manner enabling their use as key potential candidates for the fabrication of scaled optoelectronic devices and thin film transistors.

Shuttle-like CeO2/g-C3N4 composite combined with persulfate for the enhanced photocatalytic degradation of norfloxacin under visible light

In this work, the shuttle-like CeO₂ modified g-C₃N₄ composite was synthesized and was combined with persulfate (PS) for the efficient photocatalytic degradation of norfloxacin (NOR) under visible light. Scanning and transmission electron microscopy (SEM and TEM), X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) emission spectra were used to characterize the structural and optical properties of the as-prepared catalysts. Active species trapping experiments demonstrated that additional sulfate radicals (·SO₄^-) formed upon the addition of PS which could cooperate with superoxide radicals (O₂^-), holes (h⁺) and hydroxyl radicals (OH) to decompose NOR. Singlet oxygen (¹O₂) was also formed during the reaction and acted as an important active species. The degradation products of NOR were also identified and analyzed by using LC-MS technology, and the possible degradation mechanism and pathways were proposed and discussed. This work indicated that the shuttle-like CeO₂ modified g-C₃N₄ coupled with PS displayed promising applications in the field of pharmaceutical wastewater purification.

Urea assisted ceria nanocubes for efficient removal of malachite green organic dye from aqueous system

This study describes a simple, high-yield, rapid, and inexpensive route for the synthesis of cubic shape-like cerium oxide nanocubes (CeO2 NCs) using different urea concentrations (0.5, 1.0, and 2.0 g) by the hydrothermal method. The synthesized nanocubes (NCs) are labeled as CeO2 NCs-0.5, CeO2 NCs-1.0, and CeO2 NCs-2.0, corresponding to 0.5, 1.0, and 2.0 g of urea, respectively. The synthesized NCs were characterized by FT-IR, UV-visible, XRD, XPS, SEM and HR-TEM analysis. The synthesized NCs were cubic in shape with average sizes of 12, 12, and 13 nm for the CeO2 NCs-0.5, CeO2 NCs-1.0, and CeO2 NCs-2.0, respectively, obtained by the XRD analysis. The catalytic activity of the CeO2 NCs was studied for the purpose of obtaining the reduction of malachite green (MG) in the presence of sodium borohydride (NaBH4) at room temperature.

Recent advances in metal sulfides: from controlled fabrication to electrocatalytic, photocatalytic and photoelectrochemical water splitting and beyond

This review describes an in-depth overview and knowledge on the variety of synthetic strategies for forming metal sulfides and their potential use to achieve effective hydrogen generation and beyond.

Advances in nanostructures fabricated via spray pyrolysis and their applications in energy storage and conversion

This review provides insight into various nanostructures designed by spray pyrolysis and their applications in energy storage and conversion.

Construction of spindle structured CeO2 modified with rod-like attapulgite as a high-performance photocatalyst for CO2 reduction

In this study, a spindle structured CeO₂ photocatalyst modified with rod-like attapulgite (CeO₂/ATP) was successfully prepared by simple high temperature calcination.

Hierarchical ZnO Decorated with CeO2 Nanoparticles as the Direct Z-Scheme Heterojunction for Enhanced Photocatalytic Activity

Development of a high-efficiency heterojunction with an improved photocatalytic property is regarded as a promising way to decontaminate wastewater. Herein, the direct novel Z-scheme heterojunction formed between CeO₂ nanoparticles and hierarchical ZnO was synthesized through the wet chemistry method and then the heat-treatment technique. The as-synthesized ZnO/CeO₂ composites display highly enhanced photocatalytic rhodamine B (RhB) degradation compared with pristine ZnO and CeO₂. Specifically, ZnO/CeO₂-3 (mass fraction of CeO₂, 30%) shows good photostability and the best removal efficiency for photodegradated RhB, which are almost 2.5 and 1.7 times than pristine ZnO and CeO₂, respectively. On the basis of the detailed characterizations and the degradation behavior of as-prepared samples over RhB, the formed heterojunction between the hierarchical ZnO and CeO₂ nanoparticles is confirmed as the direct Z-scheme heterojunction. The heterojunction system shows fast transfer, high-efficiency separation, and long lifetime of photoinduced charge carriers, as well as enhanced redox capacity. This study affords a novel approach to construct ZnO-based Z-scheme heterojunctions for the photocatalytic applications.

One-Step Synthesis of CuO-Cu2O Heterojunction by Flame Spray Pyrolysis for Cathodic Photoelectrochemical Sensing of l-Cysteine

CuO-Cu₂O heterojunction was synthesized via a one-step flame spray pyrolysis (FSP) process and employed as photoactive material in construction of a photoelectrochemical (PEC) sensing device. The surface analysis showed that CuO-Cu₂O nanocomposites in the size less than 10 nm were formed and uniformly distributed on the electrode surface. Under visible light irradiation, the CuO-Cu₂O-coated electrode exhibited admirable cathodic photocurrent response, owing to the favorable property of the CuO-Cu₂O heterojunction such as strong absorption in the visible region and effective separation of photogenerated electron-hole pairs. On the basis of the interaction of l-cysteine (l-Cys) with Cu-containing compounds via the formation of Cu-S bond, the CuO-Cu₂O was proposed as a PEC sensor for l-Cys detection. A declined photocurrent response of CuO-Cu₂O to addition of l-Cys was observed. Influence factors including CuO-Cu₂O concentration, coating amount of CuO-Cu₂O, and applied bias potential on the PEC response toward l-Cys were optimized. Under optimum conditions, the photocurrent of the proposed sensor was linearly declined with increasing the concentration of l-Cys from 0.2 to 10 μM, with a detection limit (3S/N) of 0.05 μM. Moreover, this PEC sensor displayed high selectivity, reproducibility, and stability. The potential applicability of the proposed PEC sensor was assessed in human urine samples.

Photocatalytic reduction of CO2with H2O vapor under visible light over Ce doped ZnFe2O4

The schematic mechanism of CO₂photoreduction with H₂O vapour over Ce doped ZnFe₂O₄.