Preface to the Special Issue on “Heterogeneous Photocatalysts: From Fundamentals to Innovative Applications”

Topics in Catalysis -     

Recent advances in two-dimensional transition metal dichalcogenides as photoelectrocatalyst for hydrogen evolution reaction

Hydrogen gas has been attracting significant interest as an emerging energy source that is clean, sustainable, and renewable. Primarily, it can be produced via photoelectrochemical (PEC) splitting of water using solar energy. Among the various catalysts employed for the photoreduction of water, two-dimensional transition metal dichalcogenides (2D-TMDs) are inarguably the best candidates toward industrialization because they have extraordinary physical, optical, and electric properties, and are solution-processable at low costs. In this review, we focus on the development of 2D-TMDs and their PEC properties toward the hydrogen evolution reaction. First, the synthesis and properties of 2D materials are summarized and discussed. Next, the strategies for improving the photocatalytic activity of the 2D material-based catalysts for water splitting are thoroughly investigated. Finally, the remaining challenges and direction for the future development of 2D-TMDs in PEC catalysis-derived hydrogen evolution reaction are addressed. © 2020 Society of Chemical Industry     

Combined role of SiC whiskers and graphene nano-platelets on the microstructure of spark plasma sintered ZrB2 ceramics

This research explores the sintering behavior and microstructure of ZrB₂-based materials containing graphene nano-platelets (GNPs) and SiC whiskers (SiC_w). Spark plasma sintering (SPS) process at 1900 °C was implemented to sinter the specimen, leading to a composite with 100% relative density. High-resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), field emission-electron probe microanalyzer (FE-EPMA), and high-resolution X-ray diffractometry (HRXRD) were employed to study the SPSed sample, along with the thermodynamics predictions. According to the HRXRD result and microstructural observations, the sintering process was non-reactive, which was endorsed with the XPS analysis. Furthermore, graphene presented a beneficial role for eradicating the oxide impurities in the sample during the sintering. Such oxide impurities were reduced to the original phases of SiC and ZrB₂, contributing to porosity removal. Nanostructural investigations revealed the formation of ultrathin amorphous interfaces (~10 nm) between ZrB₂/graphene phases, disordered atomic planes in graphene platelets, and dislocations in ZrB₂ grains. One reason for generating crystalline defects in the microstructure was found out to be the mismatches amongst the elastic properties of the available compounds in the system.     

Synthesis and Photocatalytic Activity of Ni–Fe Layered Double Hydroxide Modified Sulphur Doped Graphitic Carbon Nitride (SGCN/Ni–Fe LDH) Photocatalyst for 2,4-Dinitrophenol Degradation

In this work, visible light-active sulphur doped graphitic carbon nitride coupled with Ni–Fe layered double hydroxide (SGCN/Ni–Fe LDH) was prepared through co-precipitation procedure using commercially available thiourea, nickel nitrate, and ferric nitrate. The surface morphology characterization showed LDH crystallite growth onto the surface of SGCN, exploiting the delocalized π-electrons of graphitic structure to attain chemical stability. The synthesized photocatalyst exhibited 98% 2,4-dinitrophenol (DNP) photodegradation within 120 min of visible light irradiations, which was surprisingly high compared to 60 and 55% obtained for bare GCN and Ni–Fe LDH samples. This photo removal efficiency could be due to suitable bandgap energy, layered graphitic and brucite Ni–Fe layered structures, and sufficient pollutant adherence to active sites provided by incorporation of S dopant into bare GCN. The characterization results obtained by cyclic voltammetry graph photoluminescence and electrochemical impedance spectra indicated minimum charge carrier recombination due to the type-II charge transfer route along with an active generation of ?O₂^? and h⁺ as dominant reactive species participating in DNP mineralization into more unaffected inorganic ions. The photocatalytic activity enhanced in an acidic medium at optimized parameters, i.e., pH 4, photocatalyst dosage 50 mg in 50 mL solution, and DNP concentration 1.0?×?10^?4 mol/dm³, due to ionic interactions between negatively charged DNP and positive intercalated structure of Ni–Fe LDH. The as-prepared photocatalyst photodegradation ability was retained after 5 catalytic cycles, confirming its environmentally-compatible usage in water treatment.

     

BPH Sensor Network Optimization Based on Cellular Automata and Honeycomb Structure

Mobile Networks and Applications - The brown planthopper (BPH) is a crucial pest of rice in tropical zones like the Mekong Delta of Vietnam. It economically causes severe loss to the rice harvest...     

Enhanced desalination performance and arsenate removal using semi-aromatic polyamide-based pervaporation membranes by modifying with amino-acids via interfacial polymerization

In this study, the semi-aromatic polyamide membranes were synthesized by the interfacial polymerization between piperazine (PIP) monomers in the water phase and Benzene-1,3,5-tricarbonyl chloride in the organic phase. To further modify the semi-aromatic pervaporation membrane, the two amino acids, glycine, and l -lysine, were mixed with PIP monomers for interfacial polymerization. The morphology and physicochemical properties of the synthesized membranes were analyzed using Fourier transform infrared (FTIR), field emission scanning electron microscope (FE-SEM), atomic force microscope (AFM), and contact angle measurements. The results show that the semi-aromatic polyamide membranes modified by the two amino acids possess a higher hydrophilic surface and lower thickness compared to the unmodified membrane. Additionally, the permeation flux of the semi-aromatic polyamide membranes was improved by 18.6% and 38.5% as modified with glycine and l -lysine, respectively, at the operating temperature of 70°C when the rejection of both NaCl and arsenic are higher than 99.8%. Furthermore, the operating temperature significantly influenced the permeation flux, while the salt rejections were insignificantly affected. The permeation flux increases by 3.2- and 4.0-folds for glycine and lysine-modified membranes, respectively, when elevating the feed temperature from 40°C to 70°C. The highest permeation flux of 29.5 kg m⁻² h⁻¹ with a 5 wt% NaCl rejection of 99.8% was obtained at 70°C by using 0.3 wt% l -lysine modified polyamide (PA) membrane. For elimination of 1.5 mg L⁻¹ As solution at the feed temperature of 70°C, such l -lysine modified PA membrane exhibited the permeation flux of 30.5 kg m⁻² h⁻¹ and As rejection of 99.6%, respectively. This work provides a cost-saving, facile, and eco-friendly preparation method for effectively improving the permeation flux while not sacrificing the high rejection of salts of the modified membranes.     

Recent trends in development of hematite (α-Fe2O3) as an efficient photoanode for enhancement of photoelectrochemical hydrogen production by solar water splitting

Solar-assisted water splitting using photoelectrochemical (PEC) cell is an environmentally benign technology for the generation of hydrogen fuel. However, several limitations of the materials used in fabrication of PEC cell have considerably hindered its efficiency. Extensive efforts have been made to enhance the efficiency and reduce the hydrogen generation cost using PEC cells. Photoelectrodes that are stable, efficient and made of cost-effective materials with simple synthesizing methods are essential for commercially viable solar water splitting through PEC technology. To this end, hematite (α-Fe₂O₃) has been explored as an excellent photoanode material to be used in the application of PEC water oxidation owing to its suitable bandgap of 2.1 eV that can utilize almost 40% of the visible light. In this study, we have summarized the recent progress of α-Fe₂O₃ nanostructured thin films for improving the water oxidation. Strategic modifications of α-Fe₂O₃ photoanodes comprising nanostructuring, heterojunctions, surface treatment, elemental doping, and nanocomposites are highlighted and discussed. Some prospects related to the challenges and research in this innovative research area are also provided as a guiding layout in building design principles for the improvement of α-Fe₂O₃ photoanodes in photoelectrochemical water oxidation to solve the increasing environmental issues and energy crises.     

One-Pot Synthesis of Magnetite-ZnO Nanocomposite and Its Photocatalytic Activity

Topics in Catalysis - Tri-octyl-amine is known for its potential to assist fabrication of metal and metal oxides nanoparticles. In this work elucidate the synthesis of magnetite-ZnO magnetic nano...     

Microstructure–property correlation in nano-diamond and TiN added TiC-based ceramics

In this paper, the effect of TiN and nano-diamond additives on the microstructure and properties of TiC-based composites, produced by spark plasma sintering method, was investigated. The thermal conductivity of TiC ceramic was improved significantly due to the incorporation of nano-diamond additive. Although the introduction of diamond worsened the sintering behavior of the sintered TiC ceramic, it enhanced the formation of continuous network of the graphitized diamond at the grain boundaries. However, the addition of TiN to the TiC-diamond sample led to the formation of nitrogen gas at high temperatures, resulting in a semi-porous ceramic containing ~13% porosity. Furthermore, the unreacted TiN was dissolved in the matrix, creating a solid solution of Ti(C,N). Despite the beneficial influence of nano-diamond on the thermal conductivity of TiC, the incorporation of TiN and nano-diamond in TiC ceramics decreased the flexural strength and hardness.