Search Results (20)

Water pollution is a global problem that severely impacts human and environmental health, water recycling, and the economy. In Mexico, due to water scarcity, potable water contains significant amounts of heavy metals (i.e., arsenic (As)); thus, there is a need for efficient and sustainable water treatment strategies. Bismuth oxyhalides, BiOX (X = Cl, Br, I), exhibit three-dimensional (3D) porous structures suitable for efficient adsorption activity. In addition, bismuth is an abundant and biocompatible element appropriate for fabricating sustainable environmental remediation technologies, such as adsorptive BiOX nanomaterials (NMs). In this study, we examine the adsorption capacity of BiOX (X = Cl, I), BiOX-GO (GO: graphene oxide) and GO NMs to remove methylene blue (MB), methyl orange (MO) and arsenite (AsO₃³⁻) from aqueous solution. BiOCl-GO 10%, BiOI, BiOI-GO 1%, BiOI-GO 10% and GO have an enhanced adsorption capacity, removing MB (20 ppm) within one hour using a low dose of NMs (1 mg/mL). In addition, BiOX-GO NMs can be easily separated from the solution and regenerated upon visible light activation due to the photocatalytic activity of the materials. The efficiency of the NMs under study for MO removal decreases, with the GO material having the highest efficiency (96%), followed by BiOX-GO 10% (78%). BiOCl-GO 1% removes arsenic from aqueous solution at low doses and short treatment times; 5 mg As/g adsorbent takes five hours; however, at longer adsorption times (24 h), BiOI-GO 1% excels in its arsenic removal capacity. Perlite-supported BiOCl NMs exhibit a weak capacity for water treatment due to the poor mechanical strength of perlite and the amount of surface-exposed BiOCl material. For the photocatalytic removal of arsenic (oxidation–adsorption), BiOI-GO 1% excels in arsenic removal with efficiencies > 70%. Full article

Photocatalysis offers a powerful approach for water purification from toxic organics, hydrogen production, biosolids processing, and the conversion of CO₂ into useful products. Further advancements in photocatalytic technologies depend on the development of novel, highly efficient catalysts and optimized synthesis methods. This study aimed to develop a laser synthesis technique for bismuth oxyhalide nanoparticles (NPs) as efficient and multifunctional photocatalysts. Laser ablation of a Bi target in a solution containing halogen salt precursors, followed by laser plasma treatment of the resulting colloid, yielded crystalline bismuth oxyhalides (Bi_xO_yX_z, where X = Cl, Br, or I) NPs without the need for additional annealing. The composition, structure, morphology, and optical properties of the synthesized Bi_xO_yX_z (X = Cl, Br, I) NPs were characterized using XRD analysis, electron microscopy, Raman spectroscopy, and UV-Vis spectroscopy. The effect of the halogen on the photocatalytic activity of the double oxides was investigated. The materials exhibited high photocatalytic activity in the degradation of persistent model pollutants like Rhodamine B, tetracycline, and phenol. Furthermore, the Bi_xO_yX_z NPs demonstrated good efficiency and high yield in the selective oxidation of 5-hydroxymethylfurfural (5-HMF) to 2,5-furandicarboxylic acid (FDCA). The obtained results highlight the promising potential of this laser synthesis approach for producing high-performance bismuth oxyhalide photocatalysts. Full article

Thin films of BiOCl, BiOBr, and BiOI (BiOX) were deposited by thermal evaporation for their potential application in the decontamination of water and air through their photocatalytic activity, which was compared among the three. The BiOX thin films were subjected to characterization through X-ray diffraction, high-resolution transmission electron microscopy, and scanning electron microscopy. Additionally, the optical properties were determined from the diffuse reflectance spectrum obtained with a spectrophotometer. To assess the efficacy of the semiconductor films in water decontamination, the evolution of rhodamine B discoloration and its mineralization was monitored by measuring total organic carbon. The decontaminating activity in the air was evaluated in a gas reactor, measuring the conversion of NOx-type gases. The results demonstrated that the thin films of the three oxides exhibited decontaminating photocatalytic activity in both water and air. However, notable distinctions were observed in the photocatalytic activities of the three bismuth oxyhalides in water, while in air, they exhibited similarities. In aqueous environments, the mineralization percentages exhibited notable variation after 96 h, with the BiOBr film displaying a value of 9.2%/mg and the BiOCl film a value of 3.9%/mg. In contrast, the NO conversion rate in the air was approximately 0.6%/mg for the three oxyhalide films. Full article

Transition metal (TM) single-atom catalysts (SACs) have been widely applied in photocatalytic CO₂ reduction. In this work, n–p codoping engineering is introduced to account for the modulation of photocatalytic CO₂ reduction on a two-dimensional (2D) bismuth-oxyhalide-based cathode by using first-principles calculation. n–p codoping is established via the Coulomb interactions between the negatively charged TM SACs and the positively charged Cl vacancy (V_Cl) in the dopant–defect pairs. Based on the formation energy of charged defects, neutral dopant–defect pairs for the Fe, Co, and Ni SACs (P_TM⁰) and the −1e charge state of the Cu SAC-based pair (P_Cu⁻¹) are stable. The electrostatic attraction of the n–p codoping strengthens the stability and solubility of TM SACs by neutralizing the oppositely charged V_Cl defect and TM dopant. The n–p codoping stabilizes the electron accumulation around the TM SACs. Accumulated electrons modify the d-orbital alignment and shift the d-band center toward the Fermi level, enhancing the reducing capacity of TM SACs based on the d-band theory. Besides the electrostatic attraction of the n–p codoping, the P_Cu⁻¹ also accumulates additional electrons surrounding Cu SACs and forms a half-occupied d_x²_−y² state, which further upshifts the d-band center and improves photocatalytic CO₂ reduction. The metastability of Cl multivacancies limits the concentration of the n–p pairs with Cl multivacancies (P_TM@nCl (n > 1)). Positively charged centers around the P_TM@nCl (n > 1) hinders the CO₂ reduction by shielding the charge transfer to the CO₂ molecule. Full article

Carbon dioxide (CO₂) emission has been a global concern over the past few decades due to the increase in the demand of energy, a major source of which is fossil fuels. To mitigate the emission issues, as well as to find a solution for the energy needs, an ample load of research has been carried out over the past few years in CO₂ reduction by catalysis. Bismuth, being an active catalyst both photocatalytically and electrocatalytically, is an interesting material that can be formed into oxides, sulphides, oxyhalides, etc. Numerous works have been published based on bismuth-based materials as active catalysts for the reduction of CO₂. However, a proper understanding of the behavior of the active facets and the dependence of morphology of the different bismuth-based catalysts is an interesting notion. In this review, various bismuth-based materials will be discussed regarding their activity and charge transfer properties, based on the active facets present in them. With regard to the available literature, a summarization, including photocatalysis, electrocatalysis as well as photoelectrocatalysis, will be detailed, considering various materials with different facets and morphologies. Product selectivity, varying on morphological difference, will also be realized photoelectrochemically. Full article

Hydrotalcite/bismuth solid solution (2D/2D CoAl-LDH/BiO(OH)_XI_1−X) heterojunction photocatalysts were fabricated through a hydrothermal route. Because of their identical layered structure and interlayer hydroxides, CoAl-LDH(2D) and BiO(OH)_XI_1−X(2D) form a tightly bonded heterojunction, resulting in efficient light absorption, excitation, and carrier migration conversion. At the same time, the large specific surface area and abundant hydroxyl groups of the layered structure make the heterojunction catalyst exhibit excellent performance in the photocatalytic degradation of organic pollutants. Under visible light irradiation and in the presence of 1 g/L of the catalyst, 10 mg/L of methyl orange (MO) in water could be completely degraded within 20 min, and the degradation rate of tetracycline (TC) reached 99.23% within 5 min. CoAl-LDH/BiO(OH)_XI_1−X still maintained good photocatalytic degradation activity of tetracycline after five cycles, and the structure of the catalyst did not change. The reaction mechanism related to the degradation of TC by photocatalytic reactions was explored in detail, and the photoexcitation of the semiconductor heterojunction, as well as the subsequent free radical reaction process and the degradation pathway of TC were clarified. This work provides a promising strategy for the preparation of efficient photocatalytic materials and the development of water purification technology. Full article

Two-dimensional (2D) bismuth oxyhalides (BiOX) have attracted much attention as potential optoelectronic materials. To explore their application diversity, we herewith systematically investigate the tunable properties of 2D BiOX using first-principles calculations. Their electronic and optical properties can be modulated by changing the number of monolayers, applying strain, and/or varying the halogen composition. The band gap shrinks monotonically and approaches the bulk value, the optical absorption coefficient increases, and the absorption spectrum redshifts as the layer number of 2D BiOX increases. The carrier transport property can be improved by applying tensile strain, and the ability of photocatalytic hydrogen evolution can be obtained by applying compressive strain. General strain engineering will be effective in linearly tuning the band gap of BiOX in a wide strain range. Strain, together with halogen composition variation, can tune the optical absorption spectrum to be on demand in the range from visible to ultraviolet. This suggests that 2D BiOX materials can potentially serve as tunable novel photodetectors, can be used to improve clean energy techniques, and have potential in the field of flexible optoelectronics. Full article

Recent studies have demonstrated that bismuth oxyhalides with a 2D structure inhibit the recombination of electron–hole pairs. Further, perovskite-like strontium bismuth-based compounds with a special layered Sillen X1 structure have shown potential for use as effective visible-light photocatalysts. Here, a series of strontium bismuth oxyhalide composites were prepared under different calcination conditions. The sample compositions were controlled by modulating the calcination temperature and the secondary calcination time. The synthesised catalysts were characterised by various techniques to identify the product compositions. Under visible-light irradiation, the degradation efficiencies and photocatalytic activities of the different catalysts towards rhodamine B (RhB) and 2-hydroxybenzoic acid (2-HBA) were measured via UV–Vis PDA and electron paramagnetic resonance analyses. To explore the degradation mechanism, scavengers were utilised to detect the radicals produced in the photodegradation test. SrBiO₂Cl exhibited the best RhB degradation efficiency, of 0.0685 h⁻¹, and SrBiO₂Br exhibited a rate of 0.0984 h⁻¹. At 25 °C and 1 atm, the CO₂–CH₄ photocatalytic conversion efficiencies of the optimised SrBiO₂Cl and SrBiO₂Br samples increased to 0.037 and 0.053 μmol g⁻¹ h⁻¹, respectively. The findings confirm that the catalysts are highly recyclable and effective for environmental remediation, achieving the objectives of green chemistry. Full article

The use of visible-light-driven photocatalysts in wastewater treatment, photoreduction of CO₂, green solar fuels, and solar cells has elicited substantial research attention. Bismuth oxyhalide and its derivatives are a group of visible-light photocatalysts that can diminish electron–hole recombination in layered structures and boost photocatalytic activity. The energy bandgap of these photocatalysts lies in the range of visible light. A simple hydrothermal method was applied to fabricate a series of bismuth oxychloride/bismuth oxyiodide/grafted graphitic carbon nitride (BiO_mCl_n/BiO_pI_q/g-C₃N₄) sheets with different contents of g-C₃N₄. The fabricated sheets were characterized through XRD, TEM, SEM-EDS, XPS, UV-vis DRS, PL, and BET. The conversion efficiency of CO₂ reduction to CH₄ of BiO_mCl_n/BiO_pI_q of 4.09 μmol g⁻¹ can be increased to 39.43 μmol g⁻¹ by compositing with g-C₃N₄. It had an approximately 9.64 times improvement. The photodegradation rate constant for crystal violet (CV) dye of BiO_mCl_n/BiO_pI_q of k = 0.0684 can be increased to 0.2456 by compositing with g-C₃N₄. It had an approximately 3.6 times improvement. The electron paramagnetic resonance results and the quenching effects indicated that ¹O₂, •OH, h⁺, and •O₂⁻ were active species in the aforementioned photocatalytic degradation. Because of their heterojunction, the prepared ternary nanocomposites possessed the characteristics of a heterojunction of type II band alignment. Full article

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. Full article

Well-dispersed and uniform porous ellipsoidal-shaped bismuth oxyhalides (nominal composition: 80%BiOCl/20%BiOI) microspheres were obtained by a facile solvothermal method, in which process the use of polyvinylpyrrolidone (PVP) as template agent was found to be crucial. At 150 °C, elliptical porous particles with a particle size of 0.79 μm were formed. Instead of forming solid solutions, the study of X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) shows that the prepared 80%BiOCl/20%BiOI microspheres are composite of BiOCl and BiOI in nature and the obtained crystallite size is about 5.6 nm. The optical bandgap of 80%BiOCl/20%BiOI was measured to be 2.93 eV, which is between the bandgap values of BiOCl and BiOI. The 80%BiOCl/20%BiOI microspheres were able to decompose various organic dyes (rhodamine B-RhB, methyl orange-MO, methylene blue-MB, methyl violet-MV) under an illuminated condition with the degradation rate in the order of RhB > MB > MV > MO, and 98% of RhB can be degraded in 90 min. Radical scavenger tests showed that photogenerated holes are the main active species for the photocatalytic decomposition of all of the tested organic dyes. Our results show that the obtained porous ellipsoidal-shaped 80%BiOCl/20%BiOI microspheres are promising for the degradation of various organic pollutants under the illumination of visible light. Full article

Cement-based materials modified with 3D BiOX (X = I, Cl) microspheres at different percentages (1, 5 and 10% by weight of the cement binder) were prepared to investigate the durability of the photocatalytic NO_x removal under outdoor conditions. Weathering—corresponding to a period of 13 months outdoors—was studied in terms of NO removal efficiency under visible and UVA light irradiation for BiOI and BiOCl mortars, respectively. Following this period, the samples were protected from the environment for four years, and NO_x removal and selectivity to nitrates were assessed. BiOI and BiOCl mortar samples were initially photocatalytically active; NO_x removal performance increased as BiOX content increased. There was good photocatalyst dispersion, and compressive strength was not significantly impacted. The BiOI mortars had nearly completely lost their activity after 5 years from casting, whereas mortars containing 10% BiOCl had maintained about 7% of initial performance. The results suggest that mortar deactivation is due to surface dirt and nitrates accumulation from NO_x oxidation on the surface rather than carbonation. An internal self-deactivation mechanism that affects BiOI in mortar matrix has also been postulated. Full article

Heterogeneous photocatalysis under visible light irradiation allows performing of selective oxofunctionalization of hydrocarbons at ambient temperature and pressure, using molecular oxygen as a sacrificial reagent and potential use of sunlight as a sustainable and low-cost energy source. In the present work, a photocatalytic material based on heterojunction of titanium dioxide and bismuth oxyiodide was used as photocatalyst on selective oxofunctionalization of cyclohexane and benzyl alcohol. The selective oxidation reactions were performed in a homemade photoreactor equipped with a metal halide lamp and injected air as a source of molecular oxygen. The identified oxidized products obtained from oxofunctionalization of cyclohexane were cyclohexanol and cyclohexanone. On the other hand, the product obtained from oxofunctionalization of benzyl alcohol was benzaldehyde. The yield obtained with BiOI/TiO₂ photocatalysts was higher than that obtained with pure bismuth oxyiodide. The higher performance of this material with respect to pure BiOI was attributed to its higher specific area. Full article

Semiconductor-based photocatalysis has been identified as an encouraging approach for solving the two main challenging problems, viz., remedying our polluted environment and the generation of sustainable chemical energy. Stoichiometric and non-stoichiometric bismuth oxyhalides (BiOX and Bi_xO_yX_z where X = Cl, Br, and I) are a relatively new class of semiconductors that have attracted considerable interest for photocatalysis applications due to attributes, viz., high stability, suitable band structure, modifiable energy bandgap and two-dimensional layered structure capable of generating an internal electric field. Recently, the construction of heterojunction photocatalysts, especially 2D/2D systems, has convincingly drawn momentous attention practicably owing to the productive influence of having two dissimilar layered semiconductors in face-to-face contact with each other. This review has systematically summarized the recent progress on the 2D/2D heterojunction constructed between BiOX/Bi_xO_yX_z with graphitic carbon nitride (g-C₃N₄). The band structure of individual components, various fabrication methods, different strategies developed for improving the photocatalytic performance and their applications in the degradation of various organic contaminants, hydrogen (H₂) evolution, carbon dioxide (CO₂) reduction, nitrogen (N₂) fixation and the organic synthesis of clean chemicals are summarized. The perspectives and plausible opportunities for developing high performance BiOX/Bi_xO_yX_z-g-C₃N₄ heterojunction photocatalysts are also discussed. Full article

Photocatalysis is a green technology for tackling water and air contamination. A valid alternative to the most exploited photocatalytic material, TiO₂, is bismuth oxyhalides, which feature a wider bandgap energy range and use visible radiation to attain photoexcitation. Moreover, their layered structure favors the separation of photogenerated electron–hole pairs, with an enhancement in photocatalytic activity. Controlled doping of bismuth oxyhalides with metallic bismuth nanoparticles allows for further boosting of the performance of the material. In the present work, we synthesized Y%Bi-doped BiO(Cl_0.875Br_0.125) (Y = 0.85, 1, 2, 10) photocatalysts, using cetyltrimethylammonium bromide as the bromide source and varying the chloride source to assess the impact that both length and branching of the hydrocarbon chain might have on the framing and layering of the material. A change in the amount of the reducing agent NaBH₄ allowed tuning of the percentage of metallic bismuth. After a thorough characterization (XRPD, SEM, TEM, UV-DRS, XPS), the photocatalytic activity of the catalysts was tested in the degradation of NOx under visible light, reaching a remarkable 53% conversion after 3 h of illumination for the material prepared using cetylpyridinium chloride. Full article