Facile fabrication of BiOIO3/MIL-88B heterostructured photocatalysts for removal of pollutants under visible light irradiation

Recent Advances in Photocatalytic Nanomaterials for Environmental Remediation: Strategies, Mechanisms, and Future Directions

Innovative and efficient strategies are urgently needed for wastewater treatment and environmental remediation. The photocatalytic degradation properties of photo-responsive nanomaterials (NMs) have become a prime candidate due to their low negative impact and photo-adjustability. Photocatalytic NMs vary in their degradation of different pollutants depending on the type of synthetic material, excitation light source, and physicochemical properties. Essentially, photocatalytic NMs excited by light produce reactive oxygen species (ROS) or metal ions that can degrade complex structure pollutants. Therefore, this review summarises the recent advances of photocatalytic NMs in the environmental application within the last 3 years, focusing on the development schemes, structural analyses, photocatalytic mechanisms, and the degradation effects of dyes, antibiotics, pesticides, phenolic compounds, metals, hormones, and other contaminants. The limitations and future directions are also explained. This review hopes to provide a possible pathway for the subsequent development of novel and efficient photocatalytic NMs to cope with complex and variable polluted environments.

Photocatalytic adsorption/degradation of tetracycline by S-scheme BiOI/BiOIO3 p-n heterojunction from dissociation of BiOIO3in-situ solvothermal process

The pollution of tetracycline (TC) had attracted more and more attention due to its unprecedented use and potential hazards. The S-scheme BiOI/BiOIO3 p-n heterojunction was successfully fabricated by in-situ solvothermal treatment of BiOIO3, and was used for the removal of TC from aqueous solutions. The results demonstrated that the construction of S-scheme p-n heterojunction could significantly improve the removal of TC by photocatalytic adsorption/degradation synergism. The removal rate of TC was significantly enhanced after solvothermal modification. The three main reasons for the enhanced removal efficiency were as follows: first, the light absorption range of the BiOIO3 was enhanced by solvothermal treatment; secondly, the construction of the heterojunction was beneficial to the valid separation and migration of the photo-generated carriers; finally, the adsorption of TC enhanced the speed of TC reaching the semiconductor interface and reacting with active species. Trapping tests were conducted to reveal that •O2- and 1O2 are the main reactive species for TC degradation. The nine degradation products were identified by the high performance liquid chromatography-mass spectrometry (HPLC-MS), and the three reaction pathways were deduced. A possible S-scheme p-n heterojunction photocatalytic mechanism was presented on the basis of band structures and active species capturing experiment.

Decoration of 0D Bi3NbO7 nanoparticles onto 2D BiOIO3 nanosheets as visible-light responsive S-scheme photocatalyst for photo-oxidation of antibiotics in wastewater

In this work, a new S-type hybrid composed of 2D BiOIO3 and 0D Bi3NbO7 was proposed and hybridized by a facile self-assembly strategy. The developed nanomaterials were characterized and identified by a series of sophisticated analyses, like XRD, SEM, EIS, XPS, PL, UPS, EDS, BET, M-S, TEM, HRTEM, and DRS. The photocatalytic behavior of BiOIO3/Bi3NbO7 was examined and optimized against amoxicillin (AMX) and other types of antibiotics under a variety of environmental conditions, such as visible light (150 W LED), direct sunlight, pH (3-11), catalyst dosages (20-80 mg), humic acid (0-24 mg/L), AMX concentration (10-40 mg/L), and different inorganic ions (0.05 M). The optimized BiOIO3/Bi3NbO7 hybrid attained exceptional AMX degradation activity (96.5%) under visible light (60 min), with a reaction constant of up to 0.04559 min-1, exceeding bare BiOIO3 and Bi3NbO7 by 5.57 and 5.3 folds, respectively. The obtained BiOIO3/Bi3NbO7 hybrid unclosed expanded light utilization behavior compared with neat catalysts, which originates from the powerful incorporation between BiOIO3 and Bi3NbO7 in the S-type system. The radical investigations confirmed the superiority of BiOIO3/Bi3NbO7 in generating both •OH and •O2- during the photoreaction. The novel Bi3NbO7-based heterojunction afforded robust photostability in five treatment cycles and simple charge transfer activity in the S-type route, boosting the photo-mechanism for antibiotic degradation in an efficient manner. The building of the S-scheme heterojunction between BiOIO3 and Bi3NbO7 stimulates the utilization of holes by the recombination process and promotes the overall stability of the composite. Our study introduces a new class of semiconductor heterojunctions that may contribute to the development potential of the photocatalysis sector in wastewater treatment.

A magnetically reusable Ce-MOF/GO/Fe3O4 composite for effective photocatalytic degradation of chlortetracycline

Herein, we report a novel 1/GO/Fe3O4 photocatalyst, comprising Ce(BTB)(H2O) (MOF-1, H3BTB = 1,3,5-benzenetrisbenzoic acid), graphene oxide (GO), and iron oxide (Fe3O4) for photocatalytic degradation of chlortetracycline (CTC). This design enables the effective transfer of electrons from the MOF to GO, thereby reducing the photoelectron-hole recombination rate. Therefore, the optimized 1/GO/Fe3O4 photocatalyst with H2O2 shows the highest photocatalytic activity toward CTC. The kinetic constant is 5.4 times that in the system of MOF-1 and hydrogen peroxide, which usually acted as efficient electron acceptors to improve the photocatalytic performance of MOFs. More importantly, light absorption is extended from the ultraviolet to the visible region. Furthermore, 1/GO/Fe3O4 can be quickly recycled under an applied magnetic field and displays outstanding stability and reusability. According to the radical trapping experiments and electron paramagnetic resonance results, hydroxyl radicals, superoxide radicals, and holes all contribute to excellent photocatalytic activity. The possible catalytic mechanism of 1/GO/Fe3O4 is tentatively proposed. This work aims to explore the synergistic effect between metal-organic frameworks (MOFs) and GO, and provide a theoretical basis for MOF-based composites to remove antibiotic contaminants in the environment.

Modified UiO-66-Br Microphotocatalyst with High Electron Mobility Enhances Tetracycline Degradation

In this work, the Br functional group on the ligand UiO-66-Br was modified with a Bi-O bond through the secondary solvothermal method, and the synthesis method of visible light catalyst UB (UiO-66-BiOBr) with high electron mobility was explored. The findings indicate that the effective charge transfer of the functional group-modified material UB is 2.98 times and 1.22 times that of BiOBr and traditional UiO-66/BiOBr heterojunctions, respectively. Under simulated sunlight irradiation, the removal rate of tetracycline can reach 88.71%, and the photocatalytic performance is 22.73 times higher than that of UiO-66-Br. Moreover, it maintains good adsorption and photocatalytic performance under different laboratory and actual engineering water environment conditions. In the complex water environment of municipal wastewater, the degradation effect reaches more than 80%. Finally, the decomposition pathways of TC and ecotoxicities of the intermediates were analyzed via combining theoretical calculation, LC-MS/MS, and T.E.S.T.

MOFFeCo/B-CN composites achieve efficient degradation of antibiotics in a non-homogeneous concurrent photocatalytic-persulfate activation system

We synthesized an M_FeCoB_0.4CN_x% (MOF-Fe/Co nanosheets/boron-doped g-C₃N₄) composite catalyst for enhancing the concurrent photocatalytic-persulfate activation (CPPA) system and achieved efficient degradation of antibiotics. The role of MOF-Fe/Co is to activate persulfate, while boron-doped g-C₃N₄ can generate photogenerated electrons for the reduction of Co³⁺/Fe³⁺ to enhance the regeneration of the active center. The rate constant for Tetracycline degradation by the CPPA system was 4.74 and 7.54 times higher than the photocatalytic and persulfate-activated systems, respectively. This composite was shown to be practical and economically viable for antibiotic degradation. The degradation behavior was explored based on experiments, and molecular orbitals and Fukui functions were obtained by density functional theory calculations. Mechanisms were investigated using reactive oxygen species trapping studies and electron spin resonance, and the process was explained in terms of the charge population and electron density difference of MOF-Fe/Co nanosheets. The CPPA system is an ecologically benign technology for removing antibiotic-related risks to the environment and human health.

In situ low-temperature pyrolysis fabrication type II BiOIO3/Bi4O5I2 heterostructures with enhanced visible-light-driven photooxidation activity

Novel visible-light-driven heterostructure semiconductors are considered as promising photocatalysts for the elimination of environmental organic pollutants. Herein, a solvent-assisted low-temperature in situ calcination strategy was developed to fabricate type II BiOIO₃/Bi₄O₅I₂ heterojunction by using BiOIO₃ as self-sacrificed template. The phase transition temperature of BiOIO₃ was reduced under solvent-assisted operating conditions. By controlling the elevated temperature from 200 to 300 °C, an in situ stepwise pyrolysis reaction occurred during the calcination process, which was described as BiOIO₃ → BiOIO₃/Bi₄O₅I₂ → Bi₄O₅I₂. The light absorption edge of different samples significantly red shifted from 385 to 632 nm with the increase of calcination temperature. Meanwhile, two interlocked interface lattice fringes were identified in high resolution transmission electron microscope (HRTEM) of BiOIO₃/Bi₄O₅I₂-250 composites, confirming the formation of BiOIO₃/Bi₄O₅I₂ heterojunction. The as-obtained BiOIO₃/Bi₄O₅I₂ heterojunction demonstrated the optimal photodegradation performance, which brought about 99.4% of bisphenol A (BPA) degraded within 30 min visible light (λ > 420 nm) illumination. Besides, after 5 repeated cycles, the photoactivity of BiOIO₃/Bi₄O₅I₂ heterojunction still maintained 91.5%, unfolding its high photostability. The superior photoreactivity of BiOIO₃/Bi₄O₅I₂ nanosheets was assigned to the formation of well-matched type II heterojunction, which significantly enhanced the separation and migration of photoinduced charge carriers. Superoxide radical (O₂^-) and hole (h⁺) are dominant reactive species in this photodegradation system. Based on active species quenching experiments and electron paramagnetic resonance (ESR) measurements, a possible type II heterojunction mechanism for enhanced photodegradation performance of BiOIO₃/Bi₄O₅I₂ heterostructure was proposed. This work affords an innovative method for design and construction of type II composites toward sustainable water purification.

Recent Progress of Metal-Organic Frameworks and Metal-Organic Frameworks-Based Heterostructures as Photocatalysts

In the field of photocatalysis, metal-organic frameworks (MOFs) have drawn a lot of attention. MOFs have a number of advantages over conventional semiconductors, including high specific surface area, large number of active sites, and an easily tunable porous structure. In this perspective review, different synthesis methods used to prepare MOFs and MOFs-based heterostructures have been discussed. Apart from this, the application of MOFs and MOFs-based heterostructures as photocatalysts for photocatalytic degradation of different types of pollutants have been compiled. This paper also highlights the different strategies that have been developed to modify and regulate pristine MOFs for improved photocatalytic performance. The MOFs modifications may result in better visible light absorption, effective photo-generated charge carriers (e^-/h⁺), separation and transfer as well as improved recyclability. Despite that, there are still many obstacles and challenges that need to be addressed. In order to meet the requirements of using MOFs and MOFs-based heterostructures in photocatalysis for low-cost practical applications, future development and prospects have also been discussed.