Synthesis of heterojunction photocatalysts composed of Ag 2 S quantum dots combined with Bi 4 Ti 3 O 12 nanosheets for the degradation of dyes

Interplay of Na Substitution in Magnetic Interaction and Photocatalytic Properties of Ca1-xNaxTi0.5Ta0.5O3 Perovskite Nanoparticles

This research paper delves into the enhancement of wastewater treatment through the design and synthesis of advanced photocatalytic materials, focusing on the effects of sodium (Na) substitution in Ca1-xNaxTa0.5Ti0.5O3 perovskites. By employing various analytical techniques such as X-ray diffraction, Field Emission Scanning Electron Microscopy, Transmission Electron Microscopy and UV-vis spectroscopy, the study examines the transition of these perovskites from tetragonal to orthorhombic structures and observes a reduction in Ca content with Na substitution, which also favors the cubic phase formation and inhibits secondary phases. Significantly, magnetic property analysis uncovers an unexpected ferromagnetic ordering in these perovskites, including compositions traditionally viewed as non-magnetic. The photocatalytic tests reveal a significant improvement in degrading Rhodamine B dye under visible light, particularly in samples with higher Na levels, attributed to enhanced light absorption and efficient electron processes. The study highlights the optimal Na substitution level for peak photocatalytic performance, offering valuable insights into the complex interplay between structural, magnetic, and photocatalytic properties of these perovskites, and their potential in various applications, thereby contributing to the advancement of wastewater treatment technologies.

Ag2S Nanoparticles Supported on 3D Flower-Shaped Bi2WO6 Enhanced Visible Light Catalytic Degradation of Tetracycline

A three-dimensional flower-shaped Bi2WO6 has been prepared by a hydrothermal procedure without the addition of an auxiliary agent and under neutral conditions with ultrapure water serving as solvent, and the Ag2S-Bi2WO6 composite with weight ratios of 5, 10, and 15% was prepared by a hydrothermal method. The crystallinity, morphology, mode of binding, and optical properties of the Ag2S-Bi2WO6 composite were characterized, the results of which showed that the composite had excellent dispersion, crystallinity, and purity. The composite with a weight ratio of 10% had the best photocatalytic performance, and the degradation rate of tetracycline reached 95.51% within 120 min, an increase of 27.35% over Bi2WO6. In experiments, some focus was given to the effect of the initial solution pH and the concentrations of humic acid and inorganic anions on the degradation efficiency. Based on free radical capture experiments and the semiconductor theory, the main active substances and mechanisms in the optical catalytic reaction process were studied, and speculation was given concerning the degradation pathway for the target pollutants. This study has conceived novel methods for the development of dual semiconductor systems consisting of a Ag NP composite and in doing so has provided new approaches for the development and photocatalysis for water pollution control.

Multivalent Effect of Defect Engineered Ag2S/g-C3N4 3D Porous Floating Catalyst with Enhanced Contaminant Removal Efficiency

Chlorophenols, as a major environmental pollutant, enter water systems through industrial wastewater, agricultural runoff and chemical spills, and they are stable, persistent under natural conditions, and highly hazardous to water resources. The objective of this article is to prepare Ag2S-modified C3N4 three-dimensional network photocatalyst by calcination method to use photocatalysis as an efficient, safe, and environmentally friendly method to degrade chlorophenols. Ag2S/C3N4 has an excellent visible light absorption range, low band gap, effective separation of photogenerated charges, and active free radicals production, all of which make for the enhancement of photocatalytic degradation performance of the Ag2S/C3N4 system. Under the light irradiation (λ ≥ 420 nm), the photocatalytic degradation efficiency of 2,4,6-Trichlorophenol reach 95% within 150 min, and the stable photocatalytic degradation activity can still be maintained under different pH water environment and four degradation cycles. When Ag2S is loaded on ACNs, more photogenerated electrons are generated and subsequent reactions produce highly reactive groups such as •O2- and •OH that will originally be able to continuously attack TCP molecules to degrade pollutants. Therefore, this study shows that the photocatalyst provides a novel research approach for realizing the application in the field of pollutant degradation.

Multi-catalysis of glow discharge plasma coupled with FeS2 for synergistic removal of antibiotic

Fe-based composites improved the energy utilization efficiency of plasma for removing contaminants through multi-catalysis have received much attention. However, the energy efficiency and catalytic activity are compromised by the slow transformation from Fe (Ⅲ) to Fe (Ⅱ). Here, given the electron-donating ability of reducing sulfur species, as well as the acidic environment generated by FeS₂, single FeS₂ was introduced into the glow discharge plasma (GDP) reactor for the removal of tylosin (TYL). The results showed that a significant synergistic effect between FeS₂ and GDP improved the energy efficiency of plasma and the removal efficiency of TYL (99.7%). FeS₂ boosted the generation of radicals (·OH, ·O₂^-) and nonradicals (h⁺, e^-) rather than H₂O₂ and O₃, which played an important role in TYL abatement. Moreover, the electrons donating sulfur and iron species from FeS₂ can accelerate the conversion of Fe(III) to Fe(II), which was conducive to the generation of radicals. Besides, acid solution self-adjustment resulted from the oxidation of FeS₂ improved heterogeneous Fenton reaction, the oxidation potential of ·OH and adsorption of positive charged TYL. The plausible degradation pathways of TYL were proposed in GDP/FeS₂ system. In summary, enhanced removal of TYL was mainly attributed to the catalytic pathway altered by FeS₂ through high-energy electrons, photocatalysis, heterogeneous Fenton and O₃ catalysis in the GDP system simultaneously. The strategy of integrating GDP with FeS₂ proposed in this work is expected to offer a feasible and potential technique for organic wastewater treatment.

Plasmonic Bi promotes the construction of Z-scheme heterojunction for efficient oxygen molecule activation

Reactive oxygen species (ROS) are essential to photocatalytic degradation of antibiotics in water. In this work, we prepared Ag₃PO₄/Bi@Bi₄Ti₃O₁₂ by simple in-situ reduction method and precipitation method, which improves the ability to capture visible light and increases the activity of photoinduced molecular oxygen activation, resulting in reactive oxygen species (ROS) such as superoxide radicals (•O₂^-), hydroxyl radicals (•OH), and H₂O₂. The excellent TC degradation efficiency derive from the SPR effect of the metal Bi on the surface enhances the light absorption intensity, and development of a Z-scheme heterojunction between Ag₃PO₄ and Bi₄Ti₃O₁₂ promotes the activation of molecular oxygen. A possible photodegradation mechanism of the as-prepared photocatalyst was proposed. This work provides an insight perspective to the synthesis photocatalysts with molecular oxygen activation for environmental remediation.

Bismuth-based photocatalyst for photocatalytic oxidation of flue gas mercury removal: A review

Photocatalytic oxidation method is a promising technology for solving flue gas mercury (Hg) pollution from industrial plants. Semiconductor photocatalysts have been widely applied in energy conversion and environmental remediation. However, key issues such as low light absorption capacity, wide energy band gap, and poor physicochemical stability severely limit the application of photocatalysts in practical industrial plants. In recent years, bismuth-based (Bi-based) photocatalysts, including bismuth oxide halide BiOX (X = Cl, Br or I), bismuth salt oxymetal BiVO₄, and BiOIO₃ etc., have increasingly aroused scientists' attention due to their peculiar crystalline geometric structures, tunable electronic structure and high photocatalytic performance. In present review, we firstly review the photocatalytic reaction mechanism and main photocatalytic oxidation mechanism of mercury. Secondly, the synthetic methods of Bi-based photocatalysts are summarized. Then, according to the mechanism of mercury removal, the experimental modifying approaches including heterojunction making, external atoms doping, defect creating, and crystal face regulating to promote the photocatalytic oxidation of mercury removal are summarized, as well as the determination of the band gap and electronic density of states (DOS) of Bi-based photocatalysts to elucidate the photocatalytic oxidation mechanism via density functional theory (DFT) calculation. Furthermore, constructing electronic transmission channels is an efficient way to improve the photocatalytic activity. Finally, challenges and perspectives of Bi-based photocatalyst for photocatalytic oxidation of mercury removal are presented. In addition, the excellent performance photocatalysts and efficient pollution removal equipment for mercury removal in industrial plants are still required in-depth study.

Ag-nanoparticles-loaded Ba0.85Ca0.15Ti0.9Zr0.1O3 for multicatalytic dye degradation

Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCZTO) ferroelectric ceramic loaded with Ag nanoparticles (NPs) was explored for its photo/piezocatalytic performance. The presence of Ag loading on BCZTO ceramic was confirmed using electron microscopes. X-ray photoelectron spectroscopy revealed the metallic chemical state of Ag NPs loaded on the surface of BCZTO ceramic. The absorbance spectrum of the Ag-loaded BCZTO sample showed a visible light absorption hump due to the phenomenon of surface plasmonic resonance. During the photocatalysis process, the [Formula: see text]99% of rhodamine B (RB) dye was degraded in aqueous solution using the Ag-loaded BCZTO sample, showing its promising photocatalysis activity. During the piezocatalysis process, the [Formula: see text]95% of RB dye was degraded using the Ag-loaded BCZTO sample, showing its promising piezocatalytic activity. The ·OH radical species were found responsible for the photocatalytic and piezocatalytic performance. The photo/piezocatalytic performance was found to be consistent over five cycles, indicating promising reusability of the Ag-loaded BCZTO sample.

Promoting the photocatalytic activity of Bi4Ti3O12 microspheres by incorporating iron

Small amounts of Fe(NO3)3 were added to the synthesis mixture prior to the hydrothermal synthesis of Bi4Ti3O12 microspheres. The physicochemical properties of the resulting materials were changed accordingly. The photocatalytic activities of several samples were studied through the photocatalytic degradation of organic pollutants. The samples with a theoretical Fe atomic percentage of 5.9% showed the highest photocatalytic activity among these samples. The main active species in photocatalytic degradation was demonstrated by radical capturing experiments as h+. The introduction of a suitable amount of Fe to the photocatalyst can facilitate the separation of electron-hole pairs generated upon light irradiation, inhibit their recombination efficiently, and prominently expand the light absorption region, thus leading to higher photocatalytic activity.

Enhanced photocatalytic performance by hybridization of Bi2WO6 nanoparticles with honeycomb-like porous carbon skeleton

In this work, we have assembled Bi₂WO₆ nanoparticles on the surface of honeycomb-like porous carbon skeleton (PCS) via a hydrothermal route to achieve a new type of PCS@Bi₂WO₆ hybrid composite photocatalysts. The PCS@Bi₂WO₆ hybrid structures are determined by SEM, TEM and XPS characterizations. UV-vis DRS investigation suggests an enhanced visible-light absorption of the PCS@Bi₂WO₆ composites. Transient photocurrent response, EIS and PL spectroscopy characterizations demonstrate that the composites exhibit an efficient separation of photoproduced electron/hole pairs. The photocatalytic performance of the composites were evaluated by using RhB as the model pollutant and simulated sunlight as the light source. It is revealed that the PCS@Bi₂WO₆ hybrid composites manifest much enhanced photocatalytic performance. The 5 wt%PCS@Bi₂WO₆ composite manifests the highest photocatalytic activity, which is ca. 2.1 times as large as that of bare Bi₂WO₆ nanoparticles. This can be mainly ascribed to two factors: (1) The photogenerated electron/hole pairs in Bi₂WO₆ are efficiently separated due to the electron transfer between Bi₂WO₆ and PCS; and (2) PCS induces enhanced visible-light absorption and the visible-light-excited electrons in PCS could also take part in the photocatalytic reactions.

Direct Z-scheme CaTiO3@BiOBr composite photocatalysts with enhanced photodegradation of dyes

To efficiently separate photoexcited electron/hole pairs is one of the key points for achieving excellent photocatalysts with high photocatalytic performances. To achieve this aim, here we have assembled CaTiO₃ (CTO) nanoparticles onto BiOBr microplates, thus constructing novel Z-scheme CTO@BiOBr heterojunction composite photocatalysts. Observation by scanning/transmission electron microscopy confirms the good decoration of CTO nanoparticles (15-50 nm) on the surface of BiOBr microplates (diameter 0.7-2.2 μm, thickness 70-110 nm). Simulated sunlight was used as the light source, and rhodamine B (RhB) in aqueous solution was used as the model pollutant to assess the photodegradation activity of the samples. It is demonstrated that the CTO@BiOBr composites with an appropriate CTO content exhibit much enhanced photodegradation performances. In particular, the 10%CTO@BiOBr composite with a CTO mass fraction of 10%, which photocatalyzes 99.9% degradation of RhB at 30 min of photocatalysis, has a photocatalytic activity which is about 1.8 and 23.6 times larger than that of bare BiOBr microplates and CTO nanoparticles, respectively. This can be explained as the result of the Z-scheme electron transfer and efficient separation of photoexcited electron/hole pairs, as evidenced by photoluminescence, photocurrent response, and electrochemical impedance spectroscopy investigations.

Construction of a CQDs/Ag3PO4/BiPO4 Heterostructure Photocatalyst with Enhanced Photocatalytic Degradation of Rhodamine B under Simulated Solar Irradiation

A carbon quantum dot (CQDs)/Ag₃PO₄/BiPO₄ heterostructure photocatalyst was constructed by a simple hydrothermal synthesis method. The as-prepared CQDs/Ag₃PO₄/BiPO₄ photocatalyst has been characterized in detail by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet–visible spectroscopy, and photoelectrochemical measurements. It is demonstrated that the CQDs/Ag₃PO₄/BiPO₄ composite is constructed by assembling Ag₃PO₄ fine particles and CQDs on the surface of rice-like BiPO₄ granules. The CQDs/Ag₃PO₄/BiPO₄ heterostructure photocatalyst exhibits a higher photocatalytic activity for the degradation of the rhodamine B dye than that of Ag₃PO₄, BiPO₄, and Ag₃PO₄/BiPO₄. The synergistic effects of light absorption capacity, band edge position, separation, and utilization efficiency of photogenerated carriers play the key role for the enhanced photodegradation of the rhodamine B dye.

Facile Preparation of CNT/Ag2S Nanocomposites with Improved Visible and NIR Light Photocatalytic Degradation Activity and Their Catalytic Mechanism

In this work, a series of carbon nanotubes (CNT)/Ag₂S hybrid nanocomposites were successfully prepared by a facile precipitation method. Transmission electron microscope (TEM) observation indicates that Ag₂S nanoparticles with an average particle size of ~25 nm are uniformly anchored on the surface of CNT. The photocatalytic activities of the CNT/Ag₂S nanocomposites were investigated toward the degradation of rhodamine B (RhB) under visible and near-infrared (NIR) light irradiation. It is shown that the nanocomposites exhibit obviously enhanced visible and NIR light photocatalytic activities compared with bare Ag₂S nanoparticles. Moreover, the recycling photocatalytic experiment demonstrates that the CNT/Ag₂S nanocomposites possess excellent photocatalytic stability. The photoelectrochemical and photoluminescence measurements reveal the efficient separation of photogenerated charges in the CNT/Ag₂S nanocomposites. This is the dominant reason behind the improvement of the photocatalytic activity. Based on active species trapping experiments, the possible photocatalytic mechanism of CNT/Ag₂S nanocomposites for dye degradation under visible and NIR light irradiation was proposed.

Dual-Band Plasmonic Perfect Absorber Based on Graphene Metamaterials for Refractive Index Sensing Application

We demonstrate a dual-band plasmonic perfect absorber (PA) based on graphene metamaterials. Two absorption peaks (22.5 μm and 74.5 μm) with the maximal absorption of 99.4% and 99.9% have been achieved, respectively. We utilize this perfect absorber as a plasmonic sensor for refractive index (RI) sensing. It has the figure of merit (FOM) of 10.8 and 3.2, and sensitivities of about 5.6 and 17.2 μm/RIU, respectively. Hence, the designed dual-band PA-based RI sensor exhibits good sensing performance in the infrared regime, which offers great potential applications in various biomedical, tunable spectral detecting, environmental monitoring and medical diagnostics.

Enhanced Photocatalytic Performance and Mechanism of Au@CaTiO3 Composites with Au Nanoparticles Assembled on CaTiO3 Nanocuboids

Using P25 as the titanium source and based on a hydrothermal route, we have synthesized CaTiO₃ nanocuboids (NCs) with the width of 0.3–0.5 μm and length of 0.8–1.1 μm, and systematically investigated their growth process. Au nanoparticles (NPs) of 3–7 nm in size were assembled on the surface of CaTiO₃ NCs via a photocatalytic reduction method to achieve excellent Au@CaTiO₃ composite photocatalysts. Various techniques were used to characterize the as-prepared samples, including X-ray powder diffraction (XRD), scanning/transmission electron microscopy (SEM/TEM), diffuse reflectance spectroscopy (UV-vis DRS), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Rhodamine B (RhB) in aqueous solution was chosen as the model pollutant to assess the photocatalytic performance of the samples separately under simulated-sunlight, ultraviolet (UV) and visible-light irradiation. Under irradiation of all kinds of light sources, the Au@CaTiO₃ composites, particularly the 4.3%Au@CaTiO₃ composite, exhibit greatly enhanced photocatalytic performance when compared with bare CaTiO₃ NCs. The main roles of Au NPs in the enhanced photocatalytic mechanism of the Au@CaTiO₃ composites manifest in the following aspects: (1) Au NPs act as excellent electron sinks to capture the photoexcited electrons in CaTiO₃, thus leading to an efficient separation of photoexcited electron/hole pairs in CaTiO₃; (2) the electromagnetic field caused by localized surface plasmon resonance (LSPR) of Au NPs could facilitate the generation and separation of electron/hole pairs in CaTiO₃; and (3) the LSPR-induced electrons in Au NPs could take part in the photocatalytic reactions.

Photocatalytic and Photo-Fenton Catalytic Degradation Activities of Z-Scheme Ag₂S/BiFeO₃ Heterojunction Composites under Visible-Light Irradiation

Z-scheme Ag₂S/BiFeO₃ heterojunction composites were successfully prepared through a precipitation method. The morphology and microstructure characterization demonstrate that Ag₂S nanoparticles (30⁻50 nm) are well-decorated on the surfaces of polyhedral BiFeO₃ particles (500⁻800 nm) to form Ag₂S/BiFeO₃ heterojunctions. The photocatalytic and photo-Fenton catalytic activities of the as-derived Ag₂S/BiFeO₃ heterojunction composites were evaluated by the degradation of methyl orange (MO) under visible-light irradiation. The photocatalytic result indicates that the Ag₂S/BiFeO₃ composites exhibit much improved photocatalytic activities when compared with bare Ag₂S and BiFeO₃. The optimum composite sample was observed to be 15% Ag₂S/BiFeO₃ with an Ag₂S mass fraction of 15%. Furthermore, the addition of H₂O₂ can further enhance the dye degradation efficiency, which is due to the synergistic effects of photo- and Fenton catalysis. The results of photoelectrochemical and photoluminescence measurements suggest a greater separation of the photoexcited electron/hole pairs in the Ag₂S/BiFeO₃ composites. According to the active species trapping experiments, the photocatalytic and photo-Fenton catalytic mechanisms of the Ag₂S/BiFeO₃ composites were proposed and discussed.

Growth Process and CQDs-modified Bi₄Ti₃O12 Square Plates with Enhanced Photocatalytic Performance

Bi₄Ti₃O12 square plates were synthesized via a hydrothermal route, and their growth process was systematically investigated. Carbon quantum dots (CQDs) were prepared using glucose as the carbon source, which were then assembled on the surface of Bi₄Ti₃O12 square plates via a hydrothermal route with the aim of enhancing the photocatalytic performance. XRD (X-ray powder diffraction), SEM (scanning electron microscopy), TEM (transmission electron microscopy), UV-vis DRS (diffuse reflectance spectroscopy), XPS (X-ray photoelectron spectroscopy), FTIR (Fourier transform infrared spectroscopy), PL (photoluminescence) spectroscopy, EIS (electrochemical impedance spectroscopy) and photocurrent spectroscopy were used to systematically characterize the as-prepared samples. It is demonstrated that the decoration of CQDs on Bi₄Ti₃O12 plates leads to an increased visible light absorption, slightly increased bandgap, increased photocurrent density, decreased charge-transfer resistance, and decreased PL intensity. Simulated sunlight and visible light were separately used as a light source to evaluate the photocatalytic activity of the samples toward the degradation of RhB in aqueous solution. Under both simulated sunlight and visible light irradiation, CQDs@Bi₄Ti₃O12 composites with an appropriate amount of CQDs exhibit obviously enhanced photocatalytic performance. However, the decoration of excessive CQDs gives rise to a decrease in the photocatalytic activity. The enhanced photocatalytic activity of CQDs-modified Bi₄Ti₃O12 can be attributed to the following reasons: (1) The electron transfer between Bi₄Ti₃O12 and CQDs promotes an efficient separation of photogenerated electron/hole pairs in Bi₄Ti₃O12; (2) the up-conversion photoluminescence emitted from CQDs could induce the generation of additional electron/hole pairs in Bi₄Ti₃O12; and (3) the photoexcited electrons in CQDs could participate in the photocatalytic reactions.