pH-Mediated Collective and Selective Solar Photocatalysis by a Series of Layered Aurivillius Perovskites

Solvothermal synthesis of 3D rod-shaped Ti/Al/Cr nano-oxide for photodegradation of wastewater micropollutants under sunlight: a green way to achieve SDG:6

Waterbodies are day-by-day polluted by the various colored micropollutants, e.g., azo dyes enriched (carcinogenic, non-biodegradable) colored wastewater from textile industries. Water pollution has become a serious global issue as ~ 25% of health diseases are prompted by pollution as reported by WHO. Around 1 billion people will face water scarcity by 2025 and this water crisis is also a prime focus to the UNs' sustainable development goal 6 (SDG6: clean water and sanitation). To prevent the water pollution caused by micropollutants, a mesoporous, 3D rod-like nano-oxide Ti/Al/Cr (abbreviated as TAC) has been synthesized via the solvothermal method. TAC degraded all classes of azo dyes (mono, di, tri, etc.) with > 90% efficiency under renewable energy source solar irradiation within the pH range 2-11. The detailed study was done on the photodegradation of carcinogenic di-azo dye Congo red (CR) which is banned in many countries. TAC showed 90.64 ± 2% degradation efficiency for CR at pH 7. The proposed photodegradation mechanism of CR was confirmed by the high-resolution liquid chromatography-mass spectroscopy (HRLC-MS) analysis obeying the Pirkanniemi path. The photodegradation obeyed the pseudo-1st-order kinetics and was reusable up to successive 5 cycles which can be an efficient tool to meet the UNs' SDG:6.

Efficiency and selectivity of cost-effective Zn-MOF for dye removal, kinetic and thermodynamic approach

Green synthesis of metal-organic frameworks (MOFs) has attracted a lot of attention as a crucial step for practical industrial applications. In this work, green synthesis of zinc(II) metal-organic framework (Zn-MOF) has been carried out at room temperature. The Zn metal (node) was extracted from spent domestic batteries, and the linker was benzene di-carboxylic acid (BDC). The characterization of the as-prepared Zn-MOF was accomplished by PXRD, FT-IR spectroscopy, SEM, TEM, TGA, and nitrogen adsorption at 77 K. All the characterization techniques strongly supported that as-synthesized Zn-MOF using metallic solid waste Zn is similar to that was reported in the literature. The as-prepared Zn-MOF was stable in water for 24 h without any changes in its functional groups and framework. The prepared Zn-MOF was tested for the adsorption of three dyes, two anionic dyes, aniline blue (AB), and orange II (O(II)) as well as methylene blue (MB), an example of cationic dye from aqueous solution. AB has the highest equilibrium adsorbed amount, qe, of value 55.34 mg g-1 at pH = 7 and 25 °C within 40 min. Investigation of the adsorption kinetics indicated that these adsorption processes could be described as a pseudo-second-order kinetic model. Furthermore, the adsorption process of the three dyes was described well by the Freundlich isotherm model. According to the thermodynamic parameters, the adsorption of AB on the prepared Zn-MOF was an endothermic and spontaneous process. In contrast, it was non-spontaneous and exothermic for the uptake of O(II) and MB. This study complements the business case development model of "solid waste to value-added MOFs."

Dark-Light Tandem Catalytic Oxidation of Formaldehyde over SrBi2Ta2O9 Nanosheets

Formaldehyde (HCHO), as one of the main indoor toxic pollutions, presents a great threat to human health. Hence, it is imperative to efficiently remove HCHO and create a good indoor living environment for people. Herein, a layered perovskite material SrBi2Ta2O9 (SBT), was studied for the first time and exhibited superior photocatalytic efficiency and stability compared to commercial TiO2 (P25). Furthermore, a unique dark-light tandem catalytic mechanism was constructed. In the dark reaction stage, HCHO (Lewis base) site was adsorbed on the terminal (Bi2O2)2+ layer (Lewis acid) site of SBT in the form of Lewis acid-base complexation and was gradually oxidized to CO32- intermediate (HCHO → DOM (dioxymethylene) → HCOO- → CO32-). Then, in the light reaction stage, CO32- was completely converted into CO2 and H2O (CO32- → CO2). Our study contributes to a thorough comprehension of the photocatalytic oxidation of HCHO and points out its potential for day-night continuous work applications in a natural environment.

Designed Synthesis of PDI/BiOCl-BiPO4 Composited Material for Boosted Photocatalytic Contaminant Degradation

Enhancing the photocatalytic performance for contaminant degradation to accelerate the large-scale application of photocatalysis still is an enduring challenge. Herein, ternary PDI/BiOCl-BiPO4 composited materials with the different contents of PDI were designed and constructed by the multi-step compound method. The tetracycline hydrochloride and rhodamine B were chosen as targeted pollutants to investigate the photocatalytic performance of PDI/BiOCl-BiPO4 composited materials. The structure and component of BiOCl-BiPO4 and PDI/BiOCl-BiPO4 samples were detailedly characterized by a sequence of physical and chemical characterizations. The optimized PDI/BiOCl-BiPO4 sample, namely PDI(5%)/BiOCl-BiPO4, exhibited the excellent photocatalytic activity for tetracycline hydrochloride and rhodamine B degradation. The major active species that were holes (h+) and superoxide radicals (•O2−) also can be determined in the photocatalytic degradation process by active species trapping experiments. Furthermore, the photoelectrochemical and fluorescence measurements manifest the crucial role of PDI material. It can reduce the recombination of photo-excited charge carrier and improve the separation and transfer of photo-generated electron-hole pairs, which is beneficial to the photocatalytic reaction process. It is anticipated that our work would provide a counterpart to prepare the high-efficiency composited material in heterogeneous photocatalysis.

Comparative study of ZIF-8-materials for removal of hazardous compounds using physio-chemical remediation techniques

The inherent toxicity, mutagenicity and carcinogenicity of dyes that are discharged into aquatic ecosystems, harming the health of humans and animals. ZIF-8 based composites are regarded as good adsorbents for the breakdown of dyes in order to remove or degrade them. In the course of this research, metal-organic framework materials known as ZIF-8 and its two stable composites, ZIF-8/BiCoO₃ (MZBC) and ZIF-8/BiYO₃ (MZBY), were produced via a hydrothermal process and solvothermal process, respectively, for the dangerous Congo red (CR) dye removal from the solution in water using adsorption method. According to the findings, the most significant amount of CR dye that could be adsorbed is onto MZBC, followed by MZBY and ZIF-8. The pseudo-second-order kinetic model was used effectively to match the data for adsorption behavior and was confirmed using the Langmuir isotherm equation. There is a possibility that the pH and amount of adsorbent might influence the adsorption behavior of the adsorbents. According to the experiment results, the technique featured an endothermic adsorption reaction that spontaneously occurred. The higher adsorption capability of MZBC is because of the large surface area. This results in strong interactions between the functional groups on the surface of MZBC and CR dye molecules. In addition to the electrostatic connection between functional group Zn-O-H on the surface of ZIF-8 in MZBC and the -NH₂ or SO₃ functional group areas in CR molecules, it also includes the strong π-π interaction of biphenyl rings.

Enhanced Photocatalytic Performance of Visible-Light-Driven BiVO4 Nanoparticles through W and Mo Substituting

Bismuth vanadate (BiVO4), W-doped BiVO4 (BiVO4:W), and Mo-doped BiVO4 (BiVO4:Mo) nanoparticles were synthesized at pH = 4 using a green hydrothermal method. The effects of 2 at% W or Mo doping on the microstructural and optical characteristics of as-prepared BiVO4 nanoparticles and the effect of combining particle morphology modification and impurity dopant incorporation on the visible-light-derived photocatalytic degradation of dilute Rhodamine B (RhB) solution are studied. XRD examination revealed that these obtained BiVO4-based nanoparticles had a highly crystalline and single monoclinic phase. SEM and TEM observations showed that impurity doping could modify the surface morphology, change the particle shape, and reduce the particle diameter to enlarge their specific surface area, increasing the reactive sites of the photocatalytic process. XPS and FL measurements indicated that W- and Mo-doped nanoparticles possessed higher concentrations of oxygen vacancies, which could promote the n-type semiconductor property. It was found that the BiVO4:W and BiVO4:Mo powder samples exhibited better photocatalytic activity for efficient RhB removal than that shown by pristine BiVO4 powder samples under visible light illumination. That feature can be ascribed to the larger surface area and improved concentration of photogenerated charge carriers of the former.

Hydrothermal Synthesis of Bimetallic (Zn, Co) Co-Doped Tungstate Nanocomposite with Direct Z-Scheme for Enhanced Photodegradation of Xylenol Orange

In the present study, pristine ZnWO4, CoWO4, and mixed metal Zn0.5Co0.5WO4 were synthesized through the hydrothermal process using a Teflon-lined autoclave at 180 ℃. The synthesized nanomaterials were characterized by various spectroscopic techniques, such as TEM, FTIR, UV–vis, XRD, and SEM-EDX-mapping to confirm the formation of nanocomposite material. The synthesized materials were explored as photocatalysts for the degradation of xylenol orange (XO) under a visible light source and a comparative study was explored to check the efficiency of the bimetallic co-doped nanocomposite to the pristine metal tungstate NPs. XRD analysis proved that reinforcement of Co2+ in ZnWO4 lattice results in a reduction in interplanar distance from 0.203 nm to 0.185 nm, which is reflected in its crystallite size, which reduced from 32 nm to 24 nm. Contraction in crystallite size reflects on the optical properties as the energy bandgap of ZnWO4 reduced from 3.49 eV to 3.33 eV in Zn0.5Co0.5WO4, which is due to the formation of a Z-scheme for charge transfer and enhancement in photocatalytic efficiency. The experimental results suggested that ZnWO4, CoWO4, and Zn0.5Co0.5WO4 NPs achieved a photocatalytic efficiency of 97.89%, 98.10%, and 98.77% towards XO in 120 min of visible solar light irradiation. The kinetics of photodegradation was best explained by pseudo-first-order kinetics and the values of apparent rate const (kapp) also supported the enhanced photocatalytic efficiency of mixed metal Zn0.5Co0.5WO4 NPs towards XO degradation.

Synthesis of mesoporous Fe/Al/La trimetallic oxide for photodegradation of various water-soluble dyes: Kinetic, mechanistic, and pH studies

Phase pure, trigonal, mesoporous Fe/Al/La trimetallic nano-oxide (abbreviated as FAL) was synthesized using energy efficient chemical route with bandgap 1.97 eV and S_BET = 50.02 m²/g and an average pore size of 8.95 nm for photodegradation of azo (di and tri) and thiazine class of dyes successfully. The valence band and conduction band potentials were calculated using the Mott-Schottky plot. The highest photodegradation efficiency was 93.85 ± 2% for reactive black 5 (RB5) at pH 7 under solar irradiation. The phase formation of FAL was confirmed by PXRD, TEM, and HRTEM analyses. The other characterizations include FESEM, Raman, EPR, UV, HPLC, LC-MS, etc. The presence of the metal centers and their corresponding oxidation states were confirmed by the SAEDS, elemental mapping, and XPS analyses respectively. FAL was also able to photodegrade direct blue 71 (DB71) and methylene blue (MB) under the same condition at different pH efficiently (pH 2-11). The photodegradation obeyed the pseudo-1st-order kinetics and was reusable up to 5 successive cycles. This study may be an efficient tool to meet UNs' SDG:6.

Reactive species specific RhB assisted collective photocatalytic degradation of tetracycline antibiotics with triple-layer Aurivillius perovskites

Triple-layer Aurivillius perovskites degrade tetracycline antibiotic and rhodamine B together in acidic aqueous solution. Primarily the superoxide radical generated via a semiconductor assisted dye sensitization process degrades the tetracycline.

Synergistic impacts of sonolysis aided photocatalytic degradation of water pollutant over perovskite-type CeNiO3 nanospheres

The current study reports on the preparation of perovskite-type CeNiO3 nanostructures as a sonophotocatalyst via a facile hydrothermal approach followed by annealing at 800 °C.

Preparation of Bi3Fe0.5Nb1.5O9/g-C3N4 heterojunction photocatalysts and applications in the photocatalytic degradation of 2,4-dichlorophenol in environment

The energy band relationship and the active substances were studied to determine photocatalyst accords with the Z-type transfer mechanism.

Progress and Perspectives on Aurivillius-Type Layered Ferroelectric Oxides in Binary Bi4Ti3O12-BiFeO3 System for Multifunctional Applications

Driven by potentially photo-electro-magnetic functionality, Bi-containing Aurivillius-type oxides of binary Bi4Ti3O12-BiFeO3 system with a general formula of Bin+1Fen−3Ti3O3n+3, typically in a naturally layered perovskite-related structure, have attracted increasing research interest, especially in the last twenty years. Benefiting from highly structural tolerance and simultaneous electric dipole and magnetic ordering at room temperature, these Aurivillius-phase oxides as potentially single-phase and room-temperature multiferroic materials can accommodate many different cations and exhibit a rich spectrum of properties. In this review, firstly, we discussed the characteristics of Aurivillius-phase layered structure and recent progress in the field of synthesis of such materials with various architectures. Secondly, we summarized recent strategies to improve ferroelectric and magnetic properties, consisting of chemical modification, interface engineering, oxyhalide derivatives and morphology controlling. Thirdly, we highlighted some research hotspots on magnetoelectric effect, catalytic activity, microwave absorption, and photovoltaic effect for promising applications. Finally, we provided an updated overview on the understanding and also highlighting of the existing issues that hinder further development of the multifunctional Bin+1Fen−3Ti3O3n+3 materials.

Atomic Layer Deposition of Mixed-Layered Aurivillius Phase on TiO2 Nanotubes: Synthesis, Characterization and Photoelectrocatalytic Properties

For the first time, one-dimensional phase-modulated structures consisting of two different layered Aurivillius phases with alternating five and six perovskite-like layers were obtained by atomic layer deposition (ALD) on the surface of TiO2 nanotubes (Nt). It was shown that the use of vertically oriented TiO2 Nt as the substrate and the ALD technology of a two-layer Bi2O3-FeOx sandwich-structure make it possible to obtain a layered structure due to self-organization during annealing. A detailed study by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that the coating is conformal. Raman spectroscopic analysis indicated the structure of the layered Aurivillius phases. Transient photocurrent responses under Ultraviolet-Visible (UV-Vis) light irradiation show that the ALD coating benefits the efficiency of photon excitation of electrons. The results of the photoelectrocatalytic experiments (PEC) with methyl orange degradation as a model demonstrate the significant potential of the synthesized structure as a photocatalyst. Photoluminescent measurement showed a decrease in the probability of recombination of photogenerated electron-hole pairs for ALD-coated TiO2 Nt, which demonstrates the high potential of these structures for use in photocatalytic and photoelectrochemical applications.

Coupled-substituted double-layer Aurivillius niobates: structures, magnetism and solar photocatalysis

Heterovalent coupled-substituted double-layer Aurivillius niobates, LaBi₂Nb_1.5M_0.5O₉ (M = Cr, Mn, Fe, Co), show interesting structural and magnetic characteristics in addition to sunlight-driven photocatalytic activity.