Recent Advances in LDH/g-C3N4 Heterojunction Photocatalysts for Organic Pollutant Removal

Roles of oxygen vacancies in layered double hydroxides-based catalysts for wastewater remediation: fundamentals and prospects

Wastewater globally is a significant concern for environmental health and for the sustainable management of water resources. Catalysed based advanced oxidation processes (AOP), as a relatively low operation cost and high removal efficiency of pollutants method, has a promising potential to treat the wastewater. Among the numerous catalysts, Layered Double Hydroxides (LDHs) stands out for lamellar structure, high charge density, and tuneable properties. Meanwhile, oxygen vacancies engineering could modulate the electronic properties of materials and create active centres to regulate the poor charge transfer capability of LDHs. In this regard, this review is focused on how to create and confirm the oxygen vacancies, as well as the applications of the wastewater treatment from different AOPs. It starts with the synthesized of oxygen vacancies via chemical reduction method, plasma etching method, hydrothermal treatment method, ion doping strategy. Followed by the description of characterization methods, including EPR, XPS, XAS, Raman. Finally, the role of oxygen vacancies in LDHs for contaminant removal across various systems, including photocatalysis, electrocatalysis, Fenton reactions, and sulfate radical-based processes, was thoroughly examined and analyzed.

Fabrication and Modification of Hydrotalcite-Based Photocatalysts and Their Composites for CO2 Reduction: A Critical Review

Layered double hydroxides (LDHs), which resemble hydrotalcite, are a type of materials with cationic layers and exchangeable interlayer anions. They have drawn lots of curiosity as a high-temperature CO2 adsorbent because of its quick desorption/sorption kinetics and renewability. Due to its extensive divalent or trivalent cationic metals, high anion exchange property, memory effect, adjustable behavior, bio-friendliness, easy to prepare and relatively low cost, the LDHs-based materials are becoming increasingly popular for photocatalytic CO2 reduction reaction (CO2RR). Fabrication and modification are good ways to move forward the advancement of LDHs-based catalysts, which will help chemistry and materials science make great progress. In this review we discussed structural characteristics and the methods for preparation and modification of LDHs-based photocatalysts. We also highlighted and discussed the major developments and applications in photocatalytic CO2RR as well as the photocatalytic mechanism. The goal of the present review is to give a broad summary of the various LDHs-based photocatalysts and the corresponding design strategies, which could motivate more excellent research works to explore this kind of CO2RR photocatalysts to further increase CO2 conversion yield and selectivity.

The Electronic Properties and Adsorption Performance of LDH/Graphene, and LDH/g-C3N4 for the Removal of Pharmaceutical Contaminants: A Molecular Dynamics Simulation

Water shortages and pharmaceutical pollution are two interconnected crises that pose severe threats to global health, environmental sustainability, and economic stability. Pharmaceutical pollution is widespread and has reached potentially toxic levels in over 258 rivers in 104 countries. So far, more interest has been paid towards efficient water treatment processes in recent years. In this study, we explore the efficacy of layered double hydroxide (LDH) nanocomposites with graphene and graphitic carbon nitride (g-C3N4) as promising adsorbents of pharmaceutical contaminants. The LDH nanocomposite has been designed and simulated for the first time, consisting of two layers of sodium hydroxide with a layer of graphene and g-C3N4. We investigated the adsorption performance of LDH, specifically LDH/graphene and LDH/g-C3N4, for the removal of pharmaceutical contaminants including acetaminophen (AC), caffeine (CAF), and sulfamethoxazole (SMZ). Through comprehensive molecular dynamics simulations using the reactive forcefield (ReaxFF) software, we investigated the adsorption mechanisms, kinetics, and adsorption capacity of pharmaceutical contaminants onto these nanocomposite surfaces. Our findings showed that the combination of LDH/graphene had a higher adsorption capacity for the removal of pharmaceutical contaminants than LDH/g-C3N4. At 70 Picoseconds (Ps), 124, 129, and 142 molecules of each of the pharmaceutical contaminants AC, CAF and SMZ, respectively, had been adsorbed by LDH/graphene, with a higher exothermic energy equating to -1111, -1015, and -1150 × 103 kJ/mol, respectively. On the other hand, for LDH/g-C3N4 at 70 Ps, 108, 110, and 120 molecules of AC, CAF and SMZ, respectively, had been adsorbed, with exothermic energy equating to -978, -948, and -1173 × 103 kJ/mol, respectively. Finally, we calculated the electronic properties, including the band gap and density of state of the nanocomposite materials, to check their effect on the adsorption process. In addition, the results showed that the adsorption kinetics followed a pseudo-first-order model, while the adsorption isotherms for AC, CAF and SMZ adhered to the Langmuir model.

Recent progress in ZnCr and NiCr layered double hydroxides and based photocatalysts for water treatment and clean energy production

In pursuit of advancing photocatalysts for superior performance in water treatment and clean energy generation, researchers are increasingly focusing on layered double hydroxides (LDHs) which have garnered significant attention due to their customizable properties, morphologies, distinctive 2D layered structure and flexible options for modifying anions and cations. No review has previously delved specifically into ZnCr and NiCr LDH-based photocatalysts and therefore, this review highlights the recent surge in ZnCr and NiCr-based LDHs as potential photocatalysts for their applications in water purification and renewable energy generation. The structural and fundamental characteristics of layered double hydroxides and especially ZnCr-LDHs and NiCr-LDHs are outlined. Further, the various synthesis techniques for the preparation of ZnCr-LDHs, NiCr-LDHs and their composite and heterostructure materials have been briefly discussed. The applicability of ZnCr-LDH and NiCr-LDH based photocatalysts in tackling significant issues in water treatment and sustainable energy generation is the main emphasis of this review. It focuses on photocatalytic degradation of organic pollutants in wastewater, elucidating the principles and advancements for enhancing the efficiency of these materials. It also explores their role in H2 production through water splitting, conversion of CO2 into valuable fuels and NH3 synthesis from N2, shedding light on their potential for clean energy solutions. The insights presented herein offer valuable guidance for researchers working towards sustainable solutions for environmental remediation and renewable energy generation.

Photocatalytic Degradation of Pharmaceutical Residues from Water and Sewage Effluent Using Different TiO2 Nanomaterials

Pharmaceuticals are widely used and often discharged without metabolism into the aquatic systems. The photocatalytic degradation of pharmaceutical compounds propranolol, mebeverine, and carbamazepine was studied using different titanium dioxide nanostructures suspended in water under UV and UV-visible irradiation. Among three different photocatalysts, the degradation was most effective by using Degussa P25 TiO2, followed by Hombikat UV100 and Aldrich TiO2. The photocatalytic performance was dependent on photocatalyst dosage, with an optimum concentration of 150 mg L-1. The natural aquatic colloids were shown to enhance the extent of photocatalysis, and the effect was correlated with their aromatic carbon content. In addition, the photocatalysis of pharmaceuticals was enhanced by the presence of nitrate, but inhibited by the presence of 2-propanol, indicating the importance of hydroxyl radicals. Under optimum conditions, the pharmaceuticals were rapidly degraded, with a half-life of 1.9 min, 2.1 min, and 3.2 min for propranolol, mebeverine, and carbamazepine, respectively. In treating sewage effluent samples, the photocatalytic rate constants for propranolol (0.28 min-1), mebeverine (0.21 min-1), and carbamazepine (0.15 min-1) were similar to those in water samples, demonstrating the potential of photocatalysis as a clean technology for the effective removal of pharmaceuticals from sewage effluent.