Theoretical study on the topotactic transformation and memory effect of M (II) M (III)-layered double hydroxides

In situ topotactic formation of an inorganic intergrowth bulk NiS/FeS@MgFe-LDH heterojunction to simulate CODH for the photocatalytic reduction of CO2

Enzyme-mimetic photocatalysis has been attracting much attention in bionic research, in which carbon monoxide dehydrogenase (CODH) is a suitable prototype for simulation to meet environmental and energy needs. In this study, we utilized the structural memory effect of layered double hydroxides (LDHs) to build inorganic intergrowth bulk heterojunctions (IIBHs) NiS/FeS@MgFe-LDHs via a pyrolytic topological vulcanization (PTV) method that imitated active C-clusters [Ni-4Fe-4S] in CODH. Enzyme mimicry was evaluated in terms of the microstructure and catalytic reaction site. The similarity between the microstructure of NiS/FeS@MgFe-LDHs and the CODH active group was demonstrated through XRD, XAFS and other characterisations. Subsequently, the obtained in situ irradiated X-ray photoelectron spectra and transient absorption spectra indicated the photogenerated electron transfer of the IIBH, wherein electrons finally accumulated in the conduction band of the NiS domain for the photocatalytic CO2 reduction reaction, which was similar to that of C-clusters [Ni-4Fe-4S] in which the Ni2+ ion was the reactive site. As a result, NiS/FeS@MgFe-LDHs achieved a high yield of CO at a rate of 2151.974 μmol g-1 h-1, which was 39.8 and 9.7 times more than that of NiMgFe-LDHs and NiMgFe-MMO, respectively. The study offers an innovative design route for developing IIBHs, providing novel opportunities for enzyme-mimetic photocatalysis.

Preparation of LDO@TiO2 core-shell nanosheets for enhanced photocatalytic degradation of organic pollution

TiO₂-based nanosheet materials with a core-shell structure are expected to be one of the promising photocatalysts for the degradation of organic pollution. It is a challenge to synthesize TiO₂ by the desired nucleation and growth process, so most reported TiO₂ core-shell photocatalysts are prepared using TiO₂ as a core material. Layered double hydroxides (LDHs) are considered ideal platforms to grow TiO₂in situ and further serve as additional components to improve the separation of photogenerated charge carriers. In this work, we report the design and fabrication of anatase TiO₂-coated ZnAl-layered double oxide (LDO@TiO₂) nanosheets, which involve the in situ growth of TiO₂ on ZnAl-LDH followed by subsequent calcination treatment. The resulting LDO@TiO₂ photocatalyst yields typical core-shell nanosheet morphology with a mesoporous structure, exhibiting excellent photodegradation and mineralization efficiency for organic pollution.

Remediation of carcinogenic arsenic by pyroaurite-based green adsorbent: isotherm, kinetic, mechanistic study, and applicability in real-life groundwater

The removal of the harmful carcinogen arsenic from drinking water by a green technology is a major concern in the field of environmental engineering. The sorptive profile of arsenic remediation by calcined Mg-Fe-layered double hydroxide, fabricated by a one-pot synthesis technique, was investigated to delineate its applicability in real-life water. The physicochemical properties of adsorbent, as demonstrated from spectroscopy and microscopy, which described the existence of amorphous material with significant surface roughness possess selectivity towards arsenic. The isotherm and kinetic along with thermodynamic modeling exhibited the occurrence of spontaneous (ΔG⁰ value = - 8.084 kJ/mol to - 10.942 kJ/mol), endothermic (ΔH⁰ value = 12.135 kJ/mol), and physisorption reactions (E_ad = 4.103-5.832 kJ/mol, E_a = 11.546 kJ/mol, S* = 0.0005 << 1, and ΔH_x = 9.23-16.29 kJ/mol) with high uptake rate and adsorption potential of adsorbent. The isotherm and kinetics were demonstrated by Temkin (R² = 0.944-0.969) and Elovich (R² = 0.996-0.998) models, respectively, with high statistical significance. The intraparticle diffusion model which established the rate-limiting step is the combination of both film and pore diffusions. The applicability of layered double hydroxide (LDH) material in the real-life water was confirmed by isotherm and kinetic modeling along with the regeneration/reuse potential. The adsorptive removal of arsenic by the LDH material exhibited to be a promising technique without creating any secondary hazard.