Bismuth-rich oxyhalide (Bi7O9I3-Bi4O5Br2) solid-solution photocatalysts for the degradation of phenolic compounds under visible light

HYPOTHESIS

The development of solid-solution photocatalysts with tunable bandgaps and band structures, which are significant factors that influence their photocatalytic properties, is crucial.

EXPERIMENTS

We fabricated a series of novel bismuth-rich Bi₇O₉I₃-Bi₄O₅Br₂ solid-solution photocatalysts with controlled I:Br molar ratios (denoted as B-I_xBr_1-x, x  = 0.2, 0.3, 0.4, or 0.6) via a rapid, facile, and energy-efficient microwave-heating route. The photodegradations under visible-light irradiation of the phenolic compounds (4-nitrophenol (4NP), 3-nitrophenol (3NP), and bisphenol A (BPA)), and the simultaneous photodegradation of BPA and rhodamine B (RhB) in a coexisting BPA - RhB system were investigated.

FINDINGS

The B-I_0.3Br_0.7 solid solution provided the highest photocatalytic activity toward 4NP degradation, with degradation rates 32 and 4 times higher than those of Bi₇O₉I₃ and Bi₄O₅Br₂, respectively. The photodegradation efficiency of the studied phenolic compounds followed the order BPA (97.5%) > 4NP (72.8%) > 3NP (27.5%). The RhB-sensitization mechanism significantly enhanced the photodegradation efficiency of BPA. Electrochemical measurements demonstrated the efficient separation and migration of charge carriers in the B-I_0.3Br_0.7 solid solution, which enhanced the photocatalytic activity. The B-I_0.3Br_0.7 solid solution effectively activated molecular oxygen to produce •O₂^-, which subsequently produced other reactive species, including H₂O₂ and •OH, as revealed by reactive-species trapping, nitroblue tetrazolium transformation, and o-tolidine oxidation experiments.

Silica nanolayer coated capillary by hydrothermal sol-gel process for amines separation and detection of tyramine in food products

A hydrothermal sol–gel method for reproducible formation of silica nanolayer on the wall of silica capillaries was developed for electrochromatography. The formulation was optimized by observation of uniform gel formation on an optical microscope. The variables of the formulation include types of solvent, water-TEOS ratio, CTAB and urea contents, and mixing method. The procedure produced a coating of silica ca. 100 nm thick layer on the wall of the capillary. Surface morphology of the coating was characterized by SEM, contact angle and chemical composition by FT-IR spectroscopy and X-ray powder diffraction. The coating reduced the electroosmotic mobility producing enhanced separation performance. Eight standard amines (including tyramine and benzhydrylamine, as an internal standard) were separated with peak resolution R_s ≥ 2 for all adjacent peaks and plate number N ≥ 3.0 × 10⁴ m^-1. Calibration was linear from 5 to 200 µg L^-1, with r² > 0.9985 and instrumental LOD of 4.9 μg L^-1. Five samples of food products were diluted and analyzed for the amines using the coated capillary and only tyramine was detected. Intra-day and inter-day precisions were less than 1.2%RSD. Percent recoveries of spiked tyramine in samples were 95 ± 3 to 106 ± 7% (n = 3).

Facile preparation protocol of magnetic mesoporous carbon acid catalysts via soft-template self-assembly method and their applications in conversion of xylose into furfural

Furfural is a valuable dehydration product of xylose. It has a broad spectrum of industrial applications. Various catalysts containing SO₃H have been reported for the conversion of xylose into furfural. Nevertheless, the multi-step preparation is tedious, and the catalysts are usually fine powders that are difficult to separate from the suspension. Novel magnetic mesoporous carbonaceous materials (Fe/MC) were successfully prepared via facile self-assembly in a single step. A facile subsequent hydrothermal sulfonation of Fe/MC with concentrated H₂SO₄ at 180°C gave mesoporous carbon bearing SO₃H groups (SO₃H@Fe/MC) without loss of the magnetic properties. Various techniques were employed to characterize the SO₃H@Fe/MC as a candidate catalyst. It showed strong magnetism due to its Fe particles and possessed a 243 m² g^-1 BET-specific surface area and a 90% mesopore volume. The sample contained 0.21 mmol g^-1 of SO₃H and gave a high conversion and an acceptable furfural yield and selectivity (100%, 45% and 45%, respectively) when used at 170°C for 1 h with γ-valerolactone as solvent. The catalyst was easily separated after the catalytic tests by using a magnet, confirming sufficient magneticstability. This article is part of the theme issue 'Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 2)'.

Magnetic carbon nanofiber composite adsorbent through green in-situ conversion of bacterial cellulose for highly efficient removal of bisphenol A

A magnetic carbon nanofiber sorbent was facilely synthesized from bio-based bacterial cellulose and FeCl₃via impregnation, freeze-drying, followed by pyrolysis at 700 °C, without additional activation or nanofiber fabrication. The obtained material possessed intrinsic 3D naturally fibrous and porous structure with good magnetization. The adsorption results showed that the adsorption capacity of the prepared adsorbent towards bisphenol A (BPA) was as high as 618 mg/g, outperforming other adsorbents. Moreover, recycling the adsorbent for 10 consecutive cycles retained 96% of initial adsorption efficiency. The magnetic sorbent can maintain good magnetic properties even with recycling. Hence, the use of bacterial cellulose as a renewable carbon nanofiber precursor and FeCl₃ as a source of magnetic particles, and a green pore generating agent in the present protocol, lead to a superior magnetic carbon nanofiber adsorbent with sustainable characteristics.

Double Z-scheme FeVO4/Bi4O5Br2/BiOBr ternary heterojunction photocatalyst for simultaneous photocatalytic removal of hexavalent chromium and rhodamine B

HYPOTHESIS

Fabrication of the heterojunction photocatalyst with appropriate band potentials as a promising method of inhibiting electron-hole pair recombination leading to enhanced photocatalytic properties.

EXPERIMENTS

Herein, BiOBr, Bi₄O₅Br₂, and binary BiOBr/Bi₄O₅Br₂ composite were selectively synthesized by employing a one-step microwave irradiation method. Then, double Z-scheme FeVO₄/Bi₄O₅Br₂/BiOBr ternary composites with different weight percentages (%wt) of FeVO₄ were fabricated and their photocatalytic applications were studied. The photodegradation of organic compounds (rhodamine B (RhB), methylene blue (MB) and salicylic acid (SA)), along with the photoreduction of hexavalent chromium (Cr(VI)) were investigated.

FINDINGS

Comparing with the single and binary photocatalysts, and a commercial TiO₂, the 1 %wt-FeVO₄/Bi₄O₅Br₂/BiOBr photocatalyst demonstrated superior visible-light-driven photocatalytic performance. In a Cr(VI)/RhB combined system, Cr(VI) photoreduction was further improved and coexisting RhB molecules were simultaneously degraded. Removal of Cr(VI) and RhB were maximized by adjusting both pH values and catalyst dosages. Based on UV-vis diffuse reflectance spectroscopy, photoluminescence spectroscopy, electrochemical investigations, active-species trapping, nitrotetrazolium blue transformation, and silver photo-deposition experiments, a double Z-scheme charge transfer mechanism with an RhB-sensitized effect was proposed. This special mechanism has led to significant enhancement in charge segregation and migration, along with higher redox properties of the ternary composite, which were responsible for the excellent photocatalytic activity.

Direct Z-scheme FeVO4/BiOCl heterojunction as a highly efficient visible-light-driven photocatalyst for photocatalytic dye degradation and Cr(VI) reduction

In this work, potential applications of a direct Z-scheme FeVO₄/BiOCl heterojunction for photocatalytic degradation of organic dyes (methylene blue, MB and rhodamine B, RhB) and reduction of hexavalent chromium (Cr(VI)) ion under visible light irradiation were reported. Firstly, FeVO₄ and BiOCl were synthesized by using a microwave heating method. Then, the FeVO₄/BiOCl nanocomposites with different weight percentages of FeVO₄ (1, 3, 6.25, 12.5 and 25%wt) were fabricated by a method of modified wet impregnation. The photocatalytic degradation activities of the nanocomposites were investigated in parallel with pure BiOCl and FeVO₄. Among the as-prepared nanocomposites, the FeVO₄/BiOCl nanocomposite with 6.25%wt of FeVO₄ exhibited the highest photocatalytic dye degradation efficiency; 99.8% of RhB was degraded after being irradiated for 360 min, while 87.2% of MB was degraded. Similarly, this nanocomposite photocatalytically reduced 97.8% of Cr(VI) at a pH value of 3. The superior photocatalytic activity can be ascribed to the effective visible light absorption of the FeVO₄/BiOCl heterojunction and the suppression of the recombination process of photogenerated electron-hole pairs. Additionally, the improved charge migration and separation efficiencies between FeVO₄ and BiOCl through the direct Z-scheme charge transfer pathway are involved, as evidenced by the trapping experiments, and the UV-visible diffuse reflectance (UV-vis DRS), photoluminescence spectroscopy (PL) and electrochemical impedance spectroscopy analyses. Photocatalytic mechanisms of the direct Z-scheme FeVO₄/BiOCl heterojunction for the photodegradation of RhB and photoreduction of Cr(VI) have been proposed and discussed in greater detail.

Enhanced visible-light-driven photocatalytic H2 production and Cr(vi) reduction of a ZnIn2S4/MoS2 heterojunction synthesized by the biomolecule-assisted microwave heating method

Photocatalytic applications of flower-like ZnIn₂S₄/MoS₂ composite, synthesized by biomolecule-assisted microwave heating method, in H₂ evolution and Cr(vi) reduction reactions.

Microwave synthesis of ZnIn2S4/WS2 composites for photocatalytic hydrogen production and hexavalent chromium reduction

A rapid microwave synthesis route for the fabrication of ZnIn₂S₄ powder and ZnIn₂S₄/WS₂ composites is presented.

Green and sustainable zero-waste conversion of water hyacinth (Eichhornia crassipes) into superior magnetic carbon composite adsorbents and supercapacitor electrodes

Our facile approach converts embarrassing weed to value-added products through environmentally friendly routes towards zero-waste scheme.

Magnetic carbon composites with a hierarchical structure for adsorption of tetracycline, prepared from sugarcane bagasse via hydrothermal carbonization coupled with simple heat treatment process

Sugarcane bagasse, an agricultural waste, was successfully converted into novel magnetic carbon composites by low temperature hydrothermal carbonization at 230°C for 24h, followed by heat treatment at 400°C for only 1h in air. Effects of NaOH and iron loading on the chemical properties of the composites were studied. In addition, various techniques were employed to investigate the physicochemical properties of the composites. Adsorption kinetics and isotherms were investigated with tetracycline (TC) for the magnetic composites. The magnetic carbon composite exhibited 48.35mg/g maximum adsorption capacity and was highly stable chemically and mechanically, with also good magnetic properties. The adsorption of TC by the magnetic adsorbent was mainly attributed to H-bonds and π-π interactions. The results indicate that waste sugarcane bagasse from the sugar industries can be efficiently transformed to a magnetic adsorbent for TC removal via a facile environmentally friendly method.

Controlled synthesis of barium chromate multi-layered microdiscs and their photocatalytic activity

BaCrO₄ microdiscs composed of multi-layered microplates were successfully synthesized by a facile oxalate-assisted precipitation method. Based on time-dependent experiments, a dissolution–recrystallization–self-assembly process has been proposed.

Carboxymethyl cellulose-assisted hydrothermal synthesis of PbS with nano- and micro-crystals

PbS with nano- and micro-crystals was hydrothermally synthesized from Pb(NO3)2 and thiosemicarbazide using carboxymethyl cellulose (CMC) as a template at 140, 180 and 200 degrees C for 12 h. CMC, NaOH and hydrothermal temperatures have the influence on the product morphologies characterized using a scanning electron microscope (SEM) and a transmission electron microscope (TEM). PbS (cubic) composing of Pb and S was detected using an X-ray diffractometer (XRD), a selected area electron diffraction (SAED) technique and an energy dispersive X-ray (EDX) analyzer. The interpreted patterns are in accordance with those of the simulations. Raman spectrometer revealed the presence of the vibration modes at 136, 278, 432, 602 and 967 cm(-1). Emission spectra of the products were detected at 384-388 nm using a photoluminescence (PL) spectrometer.