Synthesis and Characterization of Modified BiOCl and Their Application in Adsorption of Low-Concentration Dyes from Aqueous Solution

Synthesis of a 3D Flower-Like BiOCl/Bi-MOF Heterostructure for High-Performance Removal of Rhodamine B and Tetracycline Hydrochloride

Semiconductor materials based on bismuth metal have been extensively explored for their potential in photocatalytic applications owing to their distinctive crystal structure. Herein, we present the development of a hybrid photocatalyst, CAU-17/BiOCl, featuring a flower-like nanosheet morphology tailored for the photocatalytic degradation of organic contaminants such as rhodamine B (RhB) and tetracycline hydrochloride (TCH). The composite material is obtained by growing thin CAU-17 layers directly onto the host flower-like BiOCl nanosheets under solvothermal conditions. The optimized CAU-17/BiOCl composite possesses excellent photocatalytic performance, achieving a notable 96.0% removal rate for RhB and 78.4% for TCH after 60 and 90 min of LED light irradiation, respectively. This boosted activity is attributed to the heightened absorption of visible light caused by BiOCl and the provision of additional reaction sites due to the thin CAU-17 layers. Furthermore, the establishment of an S-scheme heterojunction mechanism enables efficient charge separation between CAU-17 and BiOCl, facilitating the separation of photoinduced electrons (e-) and holes (h+). Analysis of the degradation mechanism of RhB and TCH reveals the predominant role of superoxide radicals (•O2-), e-, and h+ in the photocatalytic degradation process. Moreover, the removal efficiency of TCH can reach approximately 64.5% after four cycles of recycling of CAU-17/BiOCl. Our work provides a facile, effective solution and a theoretically explained approach for the effective degradation of pollutants using heterojunction photocatalysts.

On the diverse utility of Cu doped ZnS/Fe3O4 nanocomposites

The global water crisis is a growing concern, with water pollution from organic dyes being a significant issue. Photocatalysis has emerged as a sustainable and renewable method for removing organic pollutants from wastewater. The study synthesized innovative (2.5, 5 and 10 wt%) Cu doped zinc sulfide/iron oxide nanocomposites using a sonochemical method, which have versatile applications in adsorption and photocatalytic degradation of organic pollutants in wastewater. The nanocomposites underwent comprehensive characterization using powder X-ray diffraction, fourier-transform infrared spectroscopy, photoluminescence spectroscopy, Ultraviolet-Visible spectrophotometer, field emission scanning electron microscopy combined with energy dispersive X-ray spectroscopy and Mott-Schottky analysis. The synthesized samples demonstrate strong adsorption ability to remove RhB and MB dyes. Afterward, we evaluated their capability to degrade Rhodamine B (RhB) dye under UV light exposure. The greatest photocatalytic efficiency was noticed when employing a UV-C lamp in combination with the 10 wt% Cu doped ZnS/Fe3O4 nanocomposite as photocatalyst (98.8% degradation after 60 min irradiation). The Langmuir-Hinshelwood model can be used to describe the pseudo first order kinetics of RhB dye photodegradation. The calculated ban gap values are 4.77, 4.67, and 4.55 eV, for (2.5, 5 and 10 wt%) Cu doped ZnS/Fe3O4, respectively. Furthermore, 10 wt% Cu doped ZnS/Fe3O4 showed good recyclability, with a degradation rate of 89% even after five cycles. Consequently, prepared samples have outstanding photocatalytic activity and can be used as useful adsorbents in water purification.

Preparation of porous silica materials using a eucalyptus template method and its efficient adsorption of methylene blue

Methylene blue (MB) is a prevalent pollutant in organic wastewater. For this research, eucalyptus wood was used as a template, into which quartz powder dissolved in NaOH was grown, resulting in a low-cost and efficient porous silica adsorbent material (PSAM). This PSAM successfully replaces expensive materials for MB removal from water. Through the application of Scanning Electron Microscopy (SEM) and Brunauer-Emmett-Teller (BET) analysis, it became evident that PSAM displays a porous slit pore structure characterized by numerous active sites, leading to an impressive maximum specific surface area of 88.05 m²/g. The central objective of this research was to investigate the impact of experimental temperature, initial dye concentration, and pH on the adsorption process. The adsorption kinetics were analyzed using the pseudo-first-order and pseudo-second-order models, as well as the Langmuir model. Remarkably, PSAM exhibited a substantial maximum adsorption capacity of 90.01 mg/g at 293 K, achieving an adsorption rate of over 85% within a mere 10-minute timeframe. The thermodynamic analysis revealed that the adsorption of MB onto PSAM was characterized by spontaneity and accompanied by heat absorption. Fourier Transform Infrared (FTIR) and SEM comparisons of PSAM before and after adsorption indicated that MB adsorption primarily occurred through electrostatic gravitational binding. In comparison to other adsorbents, PSAM exhibited exceptional efficacy in removing MB from water.

Deciphering the photoactive species-directed antibacterial mechanism of bismuth oxychloride with modulated nanoscale thickness

As an environmentally benign disinfection strategy, photocatalytic bacterial inactivation using nanoparticles involves photogenerated reactive species that cause cellular oxidative stress. Rationalising the structural performance of photocatalysts for the practical uses such as wastewater treatment has attracted significant attention; however, the contribution of reactive species to their photocatalytic antibacterial activities at the molecular and transcriptomic levels remains unclear. In this study, nontoxic bismuth oxychloride (BiOCl) photocatalysts with different nanoscale thicknesses, including nanosheets (Ns, ∼5.4 nm), nanoplates (Np, ∼1.8 nm), and ultra-nanosheets (Uns, ∼1.1 nm), were synthesised under hydrothermal conditions. Among the three samples, BiOCl Uns exhibited the most effective photocatalytic degradation efficiency with the calculated apparent rate constant of 0.0294 min^-1, ∼4 times faster than that of Ns, whereas BiOCl Ns possessed the most pronounced bactericidal effect (5.4 log inactivation). Such findings indicate the distinct role of the photoactive species responsible for photocatalytic bacterial inactivation. Moreover, transcriptome analysis of Escherichia coli after photocatalytic treatment revealed that the underlying photocatalytic antibacterial mechanism at the genetic expression level involves cellular component biosynthesis, energy metabolism, and material transportation. Notably, the differences between BiOCl Ns and BiOCl Uns were significantly enriched in purine metabolism. Therefore, the cost-effective preparation of BiOCl nanosheets with nanoscale thickness-modulated photocatalytic antibacterial activity has remarkable potential for sustainable environmental and biomedical applications.

Application of BiOX Photocatalyst to Activate Peroxydisulfate Ion-Investigation of a Combined Process for the Removal of Organic Pollutants from Water

The persulfate-based advanced oxidation processes employing heterogeneous photocatalysts to generate sulfate radicals (SO4•−) from peroxydisulfate ion (PDS, S2O82−) have been extensively investigated to remove organic pollutants. In this work, BiOX (X = Cl, Br, and I) photocatalysts were investigated to activate PDS and enhance the transformation rate of various organic substances under UV (398 nm) and Vis (400–700 nm) radiation. For BiOCl and BiOBr, in addition to excitability, the light-induced oxygen vacancies are decisive in the activity. Although without organic substances, the BiOI efficiency highly exceeds that of BiOBr and BiOCl for PDS activation (for BiOI, 15–20%, while for BiOBr and BiOCl, only 3–4% of the PDS transformed); each BiOX catalyst showed enhanced activity for 1,4-hydroquinone (HQ) transformation due to the semiquinone radical-initiated PDS activation. For sulfamethoxypyridazine (SMP), the transformation is driven by direct charge transfer, and the effect of PDS was less manifested. BiOI proved efficient for transforming various organic substances even under Vis radiation. The efficiency was enhanced by PDS addition (HQ is wholly transformed within 20 min, and SMP conversion increased from 40% to 90%) without damaging the catalyst; its activity did change over three consecutive cycles. Results related to the well-adsorbed trimethoprim (TRIM) and application of biologically treated domestic wastewater as a matrix highlighted the limiting factors of the method and visible light active photocatalyst, BiOI.

Composites of Lignin-Based Biochar with BiOCl for Photocatalytic Water Treatment: RSM Studies for Process Optimization

Textile effluents pose a massive threat to the aquatic environment, so, sustainable approaches for environmentally friendly multifunctional remediation methods degradation are still a challenge. In this study, composites consisting of bismuth oxyhalide nanoparticles, specifically bismuth oxychloride (BiOCl) nanoplatelets, and lignin-based biochar were synthesized following a one-step hydrolysis synthesis. The simultaneous photocatalytic and adsorptive remediation efficiency of the Biochar-BiOCl composites were studied for the removal of a benchmark azo anionic dye, methyl orange dye (MO). The influence of various parameters (such as catalyst dosage, initial dye concentration, and pH) on the photo-assisted removal was carried out and optimized using the Box-Behnken Design of RSM. The physicochemical properties of the nanomaterials were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, thermogravimetric analysis, nitrogen sorption, and UV-Vis diffuse reflectance spectroscopy (DRS). The maximum dye removal was observed at a catalyst dosage of 1.39 g/L, an initial dye concentration of 41.8 mg/L, and a pH of 3.15. The experiment performed under optimized conditions resulted in 100% degradation of the MO after 60 min of light exposure. The incorporation of activated biochar had a positive impact on the photocatalytic performance of the BiOCl photocatalyst for removing the MO due to favorable changes in the surface morphology, optical absorption, and specific surface area and hence the dispersion of the photo-active nanoparticles leading to more photocatalytic active sites. This study is within the frames of the design and development of green-oriented nanomaterials of low cost for advanced (waste)water treatment applications.

Investigation of the efficiency of BiOI/BiOCl composite photocatalysts using UV, cool and warm white LED light sources - Photon efficiency, toxicity, reusability, matrix effect, and energy consumption

BiOI, BiOCl, and their composites (BiOI:BiOCl) with molar ratios from 95:5 to 5:95 were synthesized and tested in the transformation of methyl orange (MO) and sulfamethoxypyridazine (SMP) antibiotic, using three various LED light sources: UV LEDs (398 nm), cool and warm white LEDs (400-700 nm). The 80:20 BiOI:BiOCl photocatalyst showed the best adsorption capacity for MO and enhanced activity compared to BiOI and BiOCl. The apparent quantum yield (Φ_app) of the MO and SMP transformation for cool and warm white light was slightly lower than for 398 nm UV radiation. The effect of methanol and 1,4-benzoquinone proved that the transformation is initiated mainly via direct charge transfer, resulting in the demethylation of MO and SO₂ extrusion from SMP. The change of photocatalytic efficiency was followed during three cycles. After the first one, the transformation rates decreased, but there was no significant difference between the second and third cycles. The decreased efficiency is most probably caused by the intermediates, whose continuous accumulation was observed during the cycles. Ecotoxicity measurements confirmed that no toxic substances were leached from the catalyst, but the transformation of both MO and SMP results in toxic intermediates. Using 80:20 BiOI:BiOCl and LED light source, the energy requirement of the removal is about half of the value determined using TiO₂ and a mercury vapor lamp. The effect of some components of wastewater (Cl^-, HCO₃^- and humic acids), pH, and two matrices on the composite photocatalysts' efficiency and stability were also investigated.

Theoretical and experimental investigations of BiOCl for electrochemical adsorption of cesium ions

BiOCl was found to have excellent electrochemical adsorption properties for cesium ions (Cs⁺) in electrochemically switched ion exchange (ESIX). In this work, BiOCl nanosheets were synthesized by a hydrothermal method and used for electrochemical adsorption of Cs⁺. The experimental results showed that BiOCl exhibited higher electrochemical adsorption selectivity for Cs⁺ than Li⁺ and Na⁺. Quantum chemical calculations based on density functional theory (DFT) were first performed to compare the adsorption and migration mechanisms of three ions Li⁺, Na⁺, and Cs⁺ in BiOCl crystals. The calculation results revealed that the excellent electrochemical adsorption performance of BiOCl for Cs⁺ is due to the interaction of embedded Cs with Cl and Bi in BiOCl crystals. This makes it have a higher adsorption energy and a lower ion migration energy barrier due to the balance of interaction forces. In this work experimental and theoretical calculations were used to systematically analyze the adsorption and migration of three ions in BiOCl, which has important guiding significance for the design of highly-efficient electroactive materials for electrochemical adsorption of Cs⁺.

Hierarchical Structure Kaolinite Nanospheres with Remarkably Enhanced Adsorption Properties for Methylene Blue

Kaolinite nanospheres with hierarchical structures were synthesized via dehydration-rehydration technique through calcined-hydrothermal route. The microstructure of samples were characterized and analyzed by diverse techniques. The results show that after hydrothermal treatment, the layered pseudo-hexagonal kaolinite particles transformed to hierarchical structure nanospheres. The hierarchical structures exhibit large specific surface area of 157.1 m² g^-1 and narrow mesoporous size distribution. The adsorption properties of kaolinite nanospheres were systematically investigated by the removal of methylene blue (MB) from water. It was found that the nanospheres can rapidly adsorb MB with a higher adsorption capacity (184.9 mg/g), and adsorption data followed Langmuir isotherm model and pseudo-second-order kinetic model. Furthermore, the adsorbent can be regenerated by washing with methanol-HCl solution and shown removal efficiency of more than 95% up to 4 cycles.

Controlled Synthesis and Selective Adsorption Properties of Pr2CuO4 Nanosheets: a Discussion of Mechanism

Tetragonal-phase Pr₂CuO₄ nanosheets with a thickness of about 60 nm were synthesized using the coordination compound methods (CCMs), then used as highly efficient selective adsorbent towards malachite green (MG) in aqueous solutions. The Pr₂CuO₄ samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse reflectance spectrum (DRS), and standard Brunauer-Emmett-Teller (BET) methods. The maximum adsorption capacity (Q_m) of as-prepared samples was determined by adsorption isotherms with different adsorbent doses (m) of 0.03-0.07 g at 298, 318, and 338 K based on the Langmuir model. When m < 0.03 g or > 0.07 g, effects of systemic mass loss and particle aggregation were discussed on the data deviation from the Langmuir model at 298 K. Based on the hydrogen bond and coordination bond, a possible mechanism of selective adsorption of MG by Pr₂CuO₄ is proposed, which was further verified by the adsorption experiments of CuO and Pr₂O₃ towards MG and competing-ion experiments. Finally, the theoretic studies were performed at DFT level to reveal the possible adsorption process.