Direct Z-scheme mediated SmVO4/UiO-66-NH2 heterojunction nanocomposite for the degradation of antibiotic tetracycline hydrochloride molecules under sunlight

A review on development and modification strategies of MOFs Z-scheme heterojunction for photocatalytic wastewater treatment, water splitting, and DFT calculations

Increasing water pollution and decreasing energy reserves have emerged as growing concerns for the environment. These pollution are due to the dangerous effects of numerous pollutants on humans and aquatic organisms, such as hydrocarbons, biphenyls, pesticides, dyes, pharmaceuticals, and metal ions. On the other hand, the need for a clean environment, finding alternatives to fossil and renewable fuels is very important. Hydrogen (H2) is regarded as a viable and promising substitute for fossil fuels, and a range of methodologies have been devised to generate this particular source of energy. Metal-organic frameworks (MOFs) are a new generation of nanoporous coordination polymers whose crystal structure is composed of the juxtaposition of organic and inorganic constituent units. Due to their flexible nature, regular structure, and high surface area, these materials have attracted much attention for removing various pollutants from water and wastewater, and water splitting. MOFs Z-scheme heterojunctions have been identified as an economical and eco-friendly method for eliminating pollutants from wastewater systems, and producing H2. Their low-cost synthesis and unique properties increase their application in various energy and environment fields. The heterojunctions possess diverse properties, such as exceptional surface area, making them ideal for degradation and separation. The development and formulation of Z-scheme heterojunctions photocatalytic systems using MOFs, which possess stable and potent redox capability, have emerged as a successful approach for addressing environmental pollution and energy shortages in recent times. Through the utilization of the benefits offered by MOFs Z-scheme heterojunctions photocatalysts, such as efficient separation and migration of charge carriers, extensive spectrum of light absorption, among other advantages, notable enhancements can be attained. This review encompasses the synthesis techniques, structure, and properties of MOFs Z-scheme heterojunctions, and their extensive use in treating various wastewaters, including dyes, pharmaceuticals, and heavy metals, and water splitting. Also, it provides an overview of the mechanisms, pathways, and various theoretical and practical aspects for MOFs Z-scheme heterojunctions. Finally, it thoroughly assesses existing challenges and suggests further research on the promising applications of MOFs Z-scheme in industrial-scale wastewater treatment.

Efficient structure tuning over the defective modulated zirconium metal organic framework with active coordinate surface for photocatalyst CO2 reduction

Structure engineering of zirconium-based metal organic frameworks (MOFs) aims to develop efficient catalysts for transforming intermittent renewable energy into value-added chemical fuels. In order to have a deeper understanding of industrial scaling, it is vital to ascertain the favourable operational parameters that are necessary for projecting at the atomic level. The proposed paradigm provides a robust basis for the efficient design of MOFs based heterogeneous photocatalysts. In this study, set of defective MOF (D-NUiO66) was effectively produced using a modular acidic method. Afterwards, the D-NUiO66 was combined with CeO2 to form the D-CeNUiO66 heterojunction for the purpose of carbon dioxide reduction. The morphological aspect of the composite investigation suggested that D-CeNUiO66 had a mesoporous structure with favourable adsorption properties. The optimized D-CeNUiO66 photocatalyst showed the high activity for the reduction of CO2 to CO, with a rate of 38.6 µmolg-1h-1 and demonstrated remarkable repeatability in terms of CO production. The incorporation of defect sites in the D-NUiO66 enhanced the light response to visible light, resulting in reduced band gap of 2.9 eV. The photoelectrochemical tests indicated that the introduction of defects in the UiO66 and coupling CeO2 in the D-CeNUiO66 composite induced fast charge transfer, therefore suppressing the charge recombination rate. This study provides valuable insights into the use of defective engineering and heterojunction approaches to metal-organic frameworks for photocatalytic applications.

In-situ construction of Zr-based metal-organic framework core-shell heterostructure for photocatalytic degradation of organic pollutants

Photocatalysis is an eco-friendly promising approach to the degradation of textile dyes. The majority of reported studies involved remediation of dyes with an initial concentration ≤50 mg/L, which was away from the existing values in textile wastewater. Herein, a simple solvothermal route was utilized to synthesize CoFe2O4@UiO-66 core-shell heterojunction photocatalyst for the first time. The photocatalytic performance of the as-synthesized catalysts was assessed through the photodegradation of methylene blue (MB) and methyl orange (MO) dyes at an initial concentration (100 mg/L). Under simulated solar irradiation, improved photocatalytic performance was accomplished by as-obtained CoFe2O4@UiO-66 heterojunction compared to bare UiO-66 and CoFe2O4. The overall removal efficiency of dyes (100 mg/L) over CoFe2O4@UiO-66 (50 mg/L) reached >60% within 180 min. The optical and photoelectrochemical measurements showed an enhanced visible light absorption capacity as well as effective interfacial charge separation and transfer over CoFe2O4@UiO-66, emphasizing the successful construction of heterojunction. The degradation mechanism was further explored, which revealed the contribution of holes (h+), superoxide (•O2 -), and hydroxyl (•OH) radicals in the degradation process, however, h+ were the predominant reactive species. This work might open up new insights for designing MOF-based core-shell heterostructured photocatalysts for the remediation of industrial organic pollutants.

Hydrolytically stable mixed ditopic linker based zirconium metal organic framework as a robust photocatalyst towards Tetracycline Hydrochloride degradation and hydrogen evolution

In the existing eco-crisis, designing and engineering an efficient as well as water stable photocatalyst for energy conversion and pollutant abatement remains crucial. In this regard, a mixed linker type zirconium metal organic framework (Zr-MOF) with terepthalic acid based ditopic linkers were utilized to design a single component photocatalyst through single step solvothermal method to utilize photons from visible light illumination towards hydrogen energy (H2) production and Tetracycline Hydrochloride (TCH) degradation. The one pot synthesized mixed linker based Zr-MOF displays visible light absorption through band gap tuning, superior exciton segregation and oxygen vacancy that cumulatively supports the enhancement in the photocatalytic output with respect to their pristine counterparts. Additionally, the X-ray photoelectron spectroscopy, optical and electrochemical studies strongly reinforces the above claims. The prepared mixed linker Zr-MOF showed superior photocatalytic H2 evolution performance of 247.88 µmol h-1 (apparent conversion efficiency; ACE = 1.9%) that is twice than its pristine Zr-MOFs. Moreover, in TCH degradation, the mixed linker MOF displays an enhanced efficacy of 91.8 % and adopts pseudo-first order type kinetics with a rate constant value of 0.032. Typically, the active species participating for the TCH photo-degradation follows the order of hydroxyl (OH.) < superoxide (O2.-) radicals. Consequently, the mixed linker Zr-MOF could be effectively used as a robust photocatalyst exhibiting boosted TCH degradation and H2 production.

Induced abundant oxygen vacancies in Sc2VO5-δ /g-C3N4 heterojunctions for enhanced photocatalytic degradation of levofloxacin

Sc2VO5-δ /g-C3N4 heterojunctions (SVCs) with abundant oxygen vacancies (OVs) were synthesized by ultrasonic exfoliation combined with the thermal etching method. The structures, OVs and spatial separation of the photogenerated carriers were systematically characterized. The results manifested that the SVCs were successfully constructed via the strong interaction between g-C3N4 (CN) and Sc2VO5-δ (SV). The SVCs possessed a higher concentration of OVs than that of pristine CN and SV. The formation of the SVC heterostructures and the optimization of the OVs were the two major factors to accelerate the separation of the charge carriers and finally to improve the photocatalysis performance. The as-prepared 10%SVC (containing 10 wt% of SV) catalyst exhibited the highest OV concentration and the best photocatalytic performance. The levofloxacin (LVX) photodegradation activity showed a positive correlation with the OV concentration. The photocatalytic degradation efficiencies were 89.1, 98.8 and 99.0% on 10%SVC for LVX, methylene blue (MB) and rhodamine B (RhB), respectively. These photodegradation processes followed the pseudo first order kinetic equation. The apparent rate constant (k app) of LVX degradation on 10%SVC was 11.0 and 7.5 times that of CN and SV. The h+, ˙OH and ˙O2 - were the major reactive species in the photodegradation process.