NiFe-Layered Double Hydroxides as a Novel Hole Repository Layer for Reinforced Visible-Light Photocatalytic Activity for Degradation of Refractory Pollutants

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

Environmental pollution has been decreased by using photocatalytic technology in conjunction with solar energy. An efficient method to obtain highly efficient photocatalysts is to build heterojunction photocatalysts by combining graphitic carbon nitride (g-C3N4) with layered double hydroxides (LDHs). In this review, recent developments in LDH/g-C3N4 heterojunctions and their applications for organic pollutant removal are systematically exhibited. The advantages of LDH/g-C3N4 heterojunction are first summarized to provide some overall understanding of them. Then, a variety of approaches to successfully assembling LDH and g-C3N4 are simply illustrated. Last but not least, certain unmet research needs for the LDH/g-C3N4 heterojunction are suggested. This review can provide some new insights for the development of high-performance LDH/g-C3N4 heterojunction photocatalysts. It is indisputable that the LDH/g-C3N4 heterojunctions can serve as high-performance photocatalysts to make new progress in organic pollutant removal.

Facile fabrication of a 2D/2D CoFe-LDH/g-C3N4 nanocomposite with enhanced photocatalytic tetracycline degradation

The widespread use of tetracycline (TC) in medicine and agriculture has caused severe pollution problems in the environment. In this work, a nanocomposite comprising of CoFe-layered double hydroxides grown on graphitic carbon nitride nanosheets (CoFe-LDH/g-C₃N₄) with a notable two-dimensional/two-dimensional (2D/2D) heterostructure was synthesized through a facile co-precipitation method. The CoFe-LDH/g-C₃N₄ nanocomposite displayed significantly improved visible-light-driven photocatalytic activity towards TC degradation, compared to pristine g-C₃N₄ and CoFe-LDH alone. The enhanced activation efficiency was a result of intimate interfacial contact, enlarged the surface area, broadened visible-light absorbance, and enhanced photogenerated electron transfer. The scavenging experiments showed that holes (h⁺) and superoxide radical anions (‧O₂^-) played a crucial role in TC degradation. Factors including the type of TCs, initial concentration of TC, presence of ions, and the type of water matrix were investigated to evaluate the practical feasibility of the nanocomposites for TC removal from antibiotics-contaminated water. The repeated tests showed that the nanocomposites possessed good stability and recyclability. This study demonstrated the feasibility of achieving photocatalytic activity enhancement of g-C₃N₄ through the formation of a 2D-2D heterostructure between LDHs and g-C₃N₄.

Synthesis of bifunctional NiFe layered double hydroxides (LDH)/Mo-doped g-C3N4 electrocatalyst for efficient methanol oxidation and seawater splitting

To boost the oxygen evolution reaction (OER) and methanol oxidation reaction (MOR) of pristine NiFe-layered double hydroxides (LDH), the NiFe-LDH/Mo-doped graphitic carbon nitride (NiFe-LDH/MoCN) heterojunction was synthesized herein through hydrothermal method. The establishment of built-in electric field in NiFe-LDH/MoCN heterojunction enhanced the electrochemical oxidation activities towards both seawater splitting and methanol oxidation, via the improving electrocatalyst surface wettability and conductivity. Almost 10-fold enhancement of turnover frequency (TOF) and electrochemical active surface area (ECSA) than pure NiFe-LDH implied more active sites to participate in catalytic reactions via Mo doping and the formation of heterostructure. Moreover, the local charge redistribution demonstrated in the NiFe-LDH/MoCN interface region may favor the adsorption of methanol and OH^- in the seawater. The present work may expound the strong coupling interaction and the establishment of built-in electric field in the interface between NiFe-LDH and semiconductor to enhance both methanol oxidation and seawater oxidation for NiFe-LDH.

Fabrication of a Covalent Organic Framework-Based Heterojunction via Coupling with ZnAgInS Nanosphere with High Photocatalytic Activity

Covalent organic frameworks (COFs) exhibit visible-light activity for the degradation of organic pollutants. However, the recombination rates of their photoinduced electron-hole pairs are relatively high, limiting their practical application. In this work, we fabricated a 1,3,5-triformylphloroglucinol (Tp) and p-phenylenediamine (Pa-1) (TpPa-1) COF-based heterojunction through coupling the TpPa-1 COF with a ZnAgInS nanosphere via a facile oil bath heating method. The results show that the prepared heterojunction exhibits outstanding catalytic activity for the degradation of high concentrations the antibiotic tetracycline (TC) and the dye rhodamine B (RhB), which is driven by simulated sunlight. Its degradation rates for RhB and TC were 30× and 18× higher than that of the pure TpPa-1 COF, respectively. The greatly enhanced photocatalytic performances can be ascribed to the formed heterojunction with good band-gap match, which promotes the migration and separation of light-induced electrons and holes and increases both light absorbance and the specific surface area. This study introduces an effective and feasible strategy for improving the photocatalytic performances of COFs via subtly integrating TpPa-1 COFs with a ZnAgInS nanosphere into an organic-inorganic hybrid. The results of the photocatalytic experiments indicate that the fabricated hybrid has a potential application in the highly efficient removal of organic pollutants.