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

Bimetallic capture sites on porous La/Bi hydroxyl double salts for efficient phosphate adsorption: Multiple active centers and excellent selective properties

The rapid development of modern agriculture aggravated water eutrophication. Therein, efficient and selective removal of phosphorus in water is the key to alleviating eutrophication. It is well known that lanthanum (La)-based material is a kind of outstanding phosphorus-locking agent. Therefore, improving the property of La-based adsorbents is a hot topic in this field. Herein, novel porous hydroxyl double salts (La/Bi-HDS) with bimetallic capture sites were prepared. The experimental result shows that La/Bi-HDS could maintain the high removal rate in the solution with a higher concentration of competing ions and the maximum P adsorption quantity of La/Bi-HDS attains 168.12 mg/g. Mechanistic studies supported by density functional theory (DFT) calculation demonstrate that introducing Bi3+ optimizes the electronic structure of La, reducing adsorption energy. In addition, the surface analysis shows that the introduction of Bi, which increases the pore size and volume of the material, improves the utilization efficiency of the active site. In a word, the introduction of Bi element as a strategy of killing two birds with one stone successfully improved the performance of La-based adsorbent. It provided a new direction for developing an efficient phosphorus-locking agent.

Controllable Crystal Growth and Improved Photocatalytic Activity of Porous Bi2O3-Bi2S3 Composite Sheets

Porous Bi₂O₃-Bi₂S₃ composite sheets were constructed through a combinational methodology of chemical bath deposition and hydrothermal reaction. The Na₂S precursor concentration in the hydrothermal solution was varied to understand the correlation between the vulcanization degree and structure evolution of the porous Bi₂O₃-Bi₂S₃ composite sheets. The control of the etching rate of the Bi₂O₃ sheet template and the regrowth rate of Bi₂S₃ crystallites via suitable sulfide precursor concentration during the hydrothermal reaction utilizes the formation of porous Bi₂O₃-Bi₂S₃ sheets. Due to the presence of Bi₂S₃ crystallites and porous structure in the Bi₂O₃-Bi₂S₃ composites, the improved visible-light absorption ability and separation efficiency of photogenerated charge carriers are achieved. Furthermore, the as-synthesized Bi₂O₃-Bi₂S₃ composite sheets obtained from vulcanization with a 0.01M Na₂S precursor display highly enhanced photocatalytic degradation toward methyl orange (MO) dyes compared with the pristine Bi₂O₃ and Bi₂S₃. The porous Bi₂O₃-Bi₂S₃ sheet system shows high surface active sites, fast transfer, high-efficiency separation of photoinduced charge carriers, and enhanced redox capacity concerning their constituent counterparts. This study affords a promising approach to constructing Bi₂O₃-based Z-scheme composites with a suitable microstructure and Bi₂O₃/Bi₂S₃ phase ratio for photoactive device applications.

CaTiO3/g-C3N4 heterojunction-based composite photocatalyst: Part I: Experimental design, kinetics, and scavenging agents' effects in photocatalytic degradation of gemifloxacin

A critical, challenging environmental issue is explored pollution of water supplies by discharging industrial/pharmaceutical/hospital/urban wastewaters into the aquatic environment. These needs introducing/developing novel photocatalysts/adsorbents/procedures for removing or mineralizing various pollutants in wastewater before discharging them into marine environments. Further, optimizing conditions to achieve the highest removal efficiency is an important issue. In this study, CaTiO₃/g-C₃N₄ (CTCN) heterostructure was synthesized and characterized by some identification techniques. The simultaneous interaction effects of the experimental variables on the boosted photocatalytic activity of CTCN in the degradation of gemifloxcacin (GMF) were studied in RSM design. The optimal values for four parameters were: catalyst dosage: 0.63 g L^-1, pH: 6.7, C_GMF: 1 mg L^-1, and irradiation time: 27.5 min, with approximately 78.2% of degradation efficiency. The quenching effects of the scavenging agents were studied to show the reactive species' relative importance in GMF photodegradation. The results illustrate that the reactive ^•OH plays a significant role, and the electron plays a minor role in the degradation process. The direct Z-scheme mechanism better described the photodegradation mechanism due to the great oxidative and reductive abilities of prepared composite photocatalysts. This mechanism is an approach to efficiently separating photogenerated charge carriers and improving the CaTiO₃/g-C₃N₄ composite photocatalyst activity. The COD has been performed to study the details of the mineralization of GMF. The pseudo-first-order rat (from the Hinshelwood model) constants of 0.046 min^-1 (t_1/2 = 15.1 min) and 0.048 min^-1 (t_1/2 = 14.4 min) were respectively obtained from the GMF photodegradation data and COD results. The prepared photocatalyst retained its activity after five reusing runs.

Photocatalytic Activity of MoS2 Nanoflower-Modified CaTiO3 Composites for Degradation of RhB under Visible Light

Nanoflower-like MoS₂ deposited on the surface of rectangular CaTiO₃(CTO) was designed and synthesized via a simple template-free strategy. Through SEM, TEM, and other characterization methods, the MoS₂ nanoflowers were confirmed to be well deposited on the surface of CTO. LED was used as the visible light source, and rhodamine B (RhB) in an aqueous solution was used as the model pollutant to assess the photodegradation activity of the samples. The results showed that the MoS₂/CaTiO₃(MCTO) composite significantly improved the photocatalytic degradation of rhodamine B (RhB) in water, compared with a single CTO, and with the MCTO-2 composite photocatalysts, 97% degradation of RhB was achieved in 180 min, and its photocatalytic activity was about 5.17 times higher than that of the bare CTO. The main reasons for enhancing photocatalytic performance are the strong interaction between the nanoflower-like MoS₂ and rectangular CTO, which can lead to the effective separation of electron transfer and photoexcited electron-hole pairs in MCTO composites. This work provides a new notion for researching an effective method of recycling catalytic materials.

Green calcium-based photocatalyst derived from waste marble powder for environmental sustainability: A review on synthesis and application in photocatalysis

Calcium, with its excellent adsorptive property and higher permissible limits in the environment, emerges as an effective wastewater treatment earth metal. Most of the catalysts, photocatalysts, and adsorbents reported in the literature have heavy metal complex, which creates a leaching problem. Majorly, precursors used for the synthesis of heterogeneous catalysts for wastewater treatment are costly. Therefore, the use of such precursors would be not suitable and feasible approach from an economic point of view. This review work is focused on giving an overview of the utilisation of calcium-based catalysts (adsorbents and photocatalyst) for the removal/degradation of various types of dye water pollutants and summarises the reported effects of calcium as a base on the removal efficiency of dopants. In this article, an extensive literature survey is presented on the various photocatalysts developed and the different syntheses involved in their preparation. As the utilisation of marble powder is a green sustainable approach, the scope of various calcium-based photocatalysts and their application is presented. This article also aims for the elementary and inclusive determination of the effect of introducing calcium as a base for different catalysts and adsorbents.

Covalent and Non-covalent Functionalized Nanomaterials for Environmental Restoration

Nanotechnology has emerged as an extraordinary and rapidly developing discipline of science. It has remolded the fate of the whole world by providing diverse horizons in different fields. Nanomaterials are appealing because of their incredibly small size and large surface area. Apart from the naturally occurring nanomaterials, synthetic nanomaterials are being prepared on large scales with different sizes and properties. Such nanomaterials are being utilized as an innovative and green approach in multiple fields. To expand the applications and enhance the properties of the nanomaterials, their functionalization and engineering are being performed on a massive scale. The functionalization helps to add to the existing useful properties of the nanomaterials, hence broadening the scope of their utilization. A large class of covalent and non-covalent functionalized nanomaterials (FNMs) including carbons, metal oxides, quantum dots, and composites of these materials with other organic or inorganic materials are being synthesized and used for environmental remediation applications including wastewater treatment. This review summarizes recent advances in the synthesis, reporting techniques, and applications of FNMs in adsorptive and photocatalytic removal of pollutants from wastewater. Future prospects are also examined, along with suggestions for attaining massive benefits in the areas of FNMs.

Microwave-assisted synthesis of defective Ca1-xAgxTi1-yCoyO3 with high photoelectrocatalytic activity for organic pollutant removal from water

CaTiO₃ is considered to be one of the most promising catalysts for the degradation of organic pollutants, but its application is limited by the wide band gap and low catalytic activity. Element doping is an effective strategy to solve these problems. Herein, a novel CaTiO₃ co-doped with Ag and Co (Ca_1-xAg_xTi_1-yCo_yO₃) was synthesized by combining co-precipitation and the microwave hydrothermal method for the first time. The crystal structure, microstructure and light absorption of the material were systematically investigated. The results showed that Ca_1-xAg_xTi_1-yCo_yO₃ had higher light absorption than pure CaTiO₃, and the band gap was reduced to 2.78 eV. First-principles calculations indicated that Ag-Ca and Co-Ti tended to form donor-acceptor defect pairs in the doping process. These defect states not only enhanced the adsorption properties, but also could be used as carrier traps to optimize the dielectric properties of CaTiO₃. In the photoelectrocatalytic system, with 0.01 g of catalyst, 98% of methylene blue in 100 mL solution (10 mg L^-1) was degraded in 150 min. In addition, Ca_1-xAg_xTi_1-yCo_yO₃ showed strong stability and excellent recyclability. The double ion co-doping technology will provide an effective strategy for improving the catalytic activity of traditional wide-band gap semiconductors.

Visible light-driven novel Bi2Ti2O7/CaTiO3 composite photocatalyst with enhanced photocatalytic activity towards NO removal

Photocatalysis is regarded as a promising technology for removal of nitrogen oxide (NO), however, the low photocatalytic efficiencies under visible light irradiation and the deactivation of the photocatalyst are as yet the significant issues that should be addressed. In this work, visible-light-driven Bi₂Ti₂O₇/CaTiO₃ heterojunction composites were synthesized by a facile in-situ hydrothermal method. The Bi₂Ti₂O₇/CaTiO₃ composites displayed superior visible light photocatalytic activity than pure CaTiO₃ and pure Bi₂Ti₂O₇ in the removal of NO at the 600 ppb level in air. Among all the composites, Bi₂Ti₂O₇/CaTiO₃ containing 20 wt% Bi₂Ti₂O₇ exhibited the best photocatalytic activity, achieving a maximum removal efficiency of 59%. The improved photocatalytic performance is mainly attributed to the strong visible-light-absorbing ability, the presence of an appropriate density of oxygen vacancy defects and the formation of heterojunction between CaTiO₃ and Bi₂Ti₂O₇, resulting in an efficient charge separation at the interface as proven by photoluminescence (PL) and photo-induced current measurements. According to trapping experiments and spin-trapping ESR analysis, the ^•O₂^- and h⁺ are the principal reactive species involved in the photocatalytic NO removal. In addition, the as-obtained Bi₂Ti₂O₇/CaTiO₃ composite showed good chemical stability, which is beneficial for practical applications in air pollution removal.

Photoactive Heterostructures: How They Are Made and Explored

In our review we consider the results on the development and exploration of heterostructured photoactive materials with major attention focused on what are the better ways to form this type of materials and how to explore them correctly. Regardless of what type of heterostructure, metal–semiconductor or semiconductor–semiconductor, is formed, its functionality strongly depends on the quality of heterojunction. In turn, it depends on the selection of the heterostructure components (their chemical and physical properties) and on the proper choice of the synthesis method. Several examples of the different approaches such as in situ and ex situ, bottom-up and top-down, are reviewed. At the same time, even if the synthesis of heterostructured photoactive materials seems to be successful, strong experimental physical evidence demonstrating true heterojunction formation are required. A possibility for obtaining such evidence using different physical techniques is discussed. Particularly, it is demonstrated that the ability of optical spectroscopy to study heterostructured materials is in fact very limited. At the same time, such experimental techniques as high-resolution transmission electron microscopy (HRTEM) and electrophysical methods (work function measurements and impedance spectroscopy) present a true signature of heterojunction formation. Therefore, whatever the purpose of heterostructure formation and studies is, the application of HRTEM and electrophysical methods is necessary to confirm that formation of the heterojunction was successful.

Mechanisms of Interfacial Charge Transfer and Photocatalytic NO Oxidation on BiOBr/SnO2 p-n Heterojunctions

In this work, hydrothermally prepared p-n heterojunction BiOBr/SnO₂ photocatalysts were applied to eliminate NO in visible light. The as-synthesized BiOBr/SnO₂ photocatalysts exhibit superior photocatalytic activity and stability through the establishment of a p-n heterojunction, resulting in a significant improvement in charge separation and transfer properties. The morphological structure and optical property of the BiOBr/SnO₂ heterojunction were also investigated comprehensively. Extended light absorption into the visible range was achieved by SnO₂ coating on the surface of the BiOBr microsphere through the constructed heterojunction between BiOBr and SnO₂, thus achieving efficient NO removal. Moreover, the transfer channels and directions of charge at the BiOBr/SnO₂ interface were determined by a combination of theoretical calculations and experimental studies. Within this p-n heterojunction, the charge in SnO₂ migrates into BiOBr through the preformed electron transfer channels, thus generating an internal electric field (IEF) between SnO₂ and BiOBr. Under the influence of IEF, the photogenerated electrons of BiOBr migrate from the conduction band (CB) to the CB of SnO₂, thus promoting the separation of electrons (e^-)-holes (h⁺) pairs. The intermediates and final products were monitored by the in situ DRIFTS technology in the process of removal of NO in visible light; hence, the oxidation pathways of NO were reasonably proposed. Meanwhile, the construction of the heterojunction not only achieves more efficient NO photocatalytic oxidation but also inhibits the production of more toxic NO₂. This work provides mechanistic insights into the interfacial charge transfer for heterojunction photocatalysts and reaction mechanism for efficient air purification.

Fabrication of ZnO@MoS2 Nanocomposite Heterojunction Arrays and Their Photoelectric Properties

In this paper, ZnO@MoS₂ core-shell heterojunction arrays were successfully prepared by the two-step hydrothermal method, and the growth mechanism was systematically studied. We found that the growth process of molybdenum disulfide (MoS₂) was sensitively dependent on the reaction temperature and time. Through an X-ray diffractometry (XRD) component test, we determined that we prepared a 2H phase MoS₂ with a direct bandgap semiconductor of 1.2 eV. Then, the photoelectric properties of the samples were studied on the electrochemical workstation. The results show that the ZnO@MoS₂ heterojunction acts as a photoanode, and the photocurrent reaches 2.566 mA under the conditions of 1000 W/m² sunshine and 0.6 V bias. The i-t curve also illustrates the perfect cycle stability. Under the condition of illumination and external bias, the electrons flow to the conduction band of MoS₂ and flow out through the external electrode of MoS₂. The holes migrate from the MoS₂ to the zinc oxide (ZnO) valence band. It is transferred to the external circuit through the glass with fluorine-doped tin oxide (FTO) together with the holes on the ZnO valence band. The ZnO@MoS₂ nanocomposite heterostructure provides a reference for the development of ultra-high-speed photoelectric switching devices, photodetector(PD) devices, and photoelectrocatalytic technologies.

Tunable Broadband Solar Energy Absorber Based on Monolayer Transition Metal Dichalcogenides Materials Using Au Nanocubes

In order to significantly enhance the absorption capability of solar energy absorbers in the visible wavelength region, a novel monolayer molybdenum disulfide (MoS₂)-based nanostructure was proposed. Local surface plasmon resonances (LSPRs) supported by Au nanocubes (NCs) can improve the absorption of monolayer MoS₂. A theoretical simulation by a finite-difference time-domain method (FDTD) shows that the absorptions of proposed MoS₂-based absorbers are above 94.0% and 99.7% at the resonant wavelengths of 422 and 545 nm, respectively. In addition, the optical properties of the proposed nanostructure can be tuned by the geometric parameters of the periodic Au nanocubes array, distributed Bragg mirror (DBR) and polarization angle of the incident light, which are of great pragmatic significance for improving the absorption efficiency and selectivity of monolayer MoS₂. The absorber is also able to withstand a wide range of incident angles, showing polarization-independence. Similar design ideas can also be implemented to other transition-metal dichalcogenides (TMDCs) to strengthen the interaction between light and MoS₂. This nanostructure is relatively simple to implement and has a potentially important application value in the development of high-efficiency solar energy absorbers and other optoelectronic devices.

A Tunable Triple-Band Near-Infrared Metamaterial Absorber Based on Au Nano-Cuboids Array

In this article, we present a design for a triple-band tunable metamaterial absorber with an Au nano-cuboids array, and undertake numerical research about its optical properties and local electromagnetic field enhancement. The proposed structure is investigated by the finite-difference time domain (FDTD) method, and we find that it has triple-band tunable perfect absorption peaks in the near infrared band (1000–2500 nm). We investigate some of structure parameters that influence the fields of surface plasmons (SP) resonances of the nano array structure. By adjusting the relevant structural parameters, we can accomplish the regulation of the surface plasmons resonance (SPR) peaks. In addition, the triple-band resonant wavelength of the absorber has good operational angle-polarization-tolerance. We believe that the excellent properties of our designed absorber have promising applications in plasma-enhanced photovoltaic, optical absorption switching and infrared modulator optical communication.

In Situ Construction of CNT/CuS Hybrids and Their Application in Photodegradation for Removing Organic Dyes

Herein, a coprecipitation method used to synthesize CuS nanostructures is reported. By varying the reaction time and temperature, the evolution of the CuS morphology between nanoparticles and nanoflakes was investigated. It was found that CuS easily crystallizes into sphere-/ellipsoid-like nanoparticles within a short reaction time (0.5 h) or at a high reaction temperature (120 °C), whereas CuS nanoflakes are readily formed at a low reaction temperature (20 °C) for a long time (12 h). Photodegradation experiments demonstrate that CuS nanoflakes exhibit a higher photodegradation performance than CuS nanoparticles for removing rhodamine B (RhB) from aqueous solution under simulated sunlight irradiation. Carbon nanotubes (CNTs) were further used to modify the photodegradation performance of a CuS photocatalyst. To achieve this aim, CNTs and CuS were integrated to form CNT/CuS hybrid composites via an in situ coprecipitation method. In the in situ constructed CNT/CuS composites, CuS is preferably formed as nanoparticles, but cannot be crystallized into nanoflakes. Compared to bare CuS, the CNT/CuS composites manifest an obviously enhanced photodegradation of RhB; notably, the 3% CNT/CuS composite with CNT content of 3% showed the highest photodegradation performance (η = 89.4% for 120 min reaction, kapp = 0.01782 min-1). To make a comparison, CuS nanoflakes and CNTs were mechanically mixed in absolute alcohol and then dried to obtain the 3% CNT/CuS-MD composite. It was observed that the 3% CNT/CuS-MD composite exhibited a slightly higher photodegradation performance (η = 92.4%, kapp = 0.0208 min-1) than the 3% CNT/CuS composite, which may be attributed to the fact that CuS maintains the morphology of nanoflakes in the 3% CNT/CuS-MD composite. The underlying enhanced photocatalytic mechanism of the CNT/CuS composites was systematically investigated and discussed.

High Quality Factor, High Sensitivity Metamaterial Graphene-Perfect Absorber Based on Critical Coupling Theory and Impedance Matching

By means of critical coupling and impedance matching theory, we have numerically simulated the perfect absorption of monolayer graphene. Through the critical coupling effect and impedance matching, we studied a perfect single-band absorption of the monolayer graphene and obtained high quality factor (Q-factor = 664.2) absorption spectrum which has an absorbance close to 100% in the near infrared region. The position of the absorption spectrum can be adjusted by changing the ratio between the radii of the elliptic cylinder air hole and the structural period. The sensitivity of the absorber can be achieved S = 342.7 nm/RIU (RIU is the per refractive index unit) and FOM = 199.2 (FOM is the figure of merit), which has great potential for development on biosensors. We believe that our research will have good application prospects in graphene photonic devices and optoelectronic devices.

Photo-Fenton Degradation of AO7 and Photocatalytic Reduction of Cr(VI) over CQD-Decorated BiFeO3 Nanoparticles Under Visible and NIR Light Irradiation

In this work, the carbon quantum dot (CQD)-decorated BiFeO3 nanoparticle photocatalysts were prepared by a hydrothermal method. The TEM observation and XPS characterization indicate that the CQDs are well anchored on the surface of BiFeO3 nanoparticles. Acid orange 7 (AO7) and hexavalent chromium (Cr(VI)) were chosen as the model pollutants to investigate the photocatalytic/photo-Fenton degradation and photocatalytic reduction performances of the as-prepared CQD/BiFeO3 composites under visible and near-infrared (NIR) light irradiation. Compared with bare BiFeO3 nanoparticles, the CQD/BiFeO3 composites exhibit significantly improved photocatalytic and photo-Fenton catalytic activities. Moreover, the composites possess good catalytic stability. The efficient photogenerated charges separation in the composites was demonstrated by the photocurrent response and electrochemical impedance spectroscopy (EIS) measurements. The main active species involved in the catalytic degradation reaction were clarified by radicals trapping and detection experiments. The underlying photocatalytic and photo-Fenton mechanisms are systematically investigated and discussed.

Carbon Quantum Dots (CQDs) Decorated Bi2O3-x Hybrid Photocatalysts with Promising NIR-Light-Driven Photodegradation Activity for AO7

In this work, Bi2O3-x with surface oxygen vacancies was prepared through the NaBH4 reduction of Bi2O3. After that, carbon quantum dots (CQDs) were deposited onto the surface of the Bi2O3-x to obtain a series of the CQDs/Bi2O3-x composites. The HRTEM and XPS characterizations of the CQDs/Bi2O3-x composites suggest that the thickness of surface oxygen vacancies could be adjusted by changing the concentration of NaBH4 solution, and the intimate contact between CQDs and the Bi2O3-x is achieved. Acid orange 7 (AO7) was adopted as the target reactant for investigating the photocatalytic degradation activities of the CQDs/Bi2O3-x composites under simulated sunlight and NIR light irradiation. It is found that the photocatalytic activities of the samples are closely related to the concentration of NaBH4 and content of CQDs. The Bi2O3-x samples exhibit enhanced simulated-sunlight-driven photocatalytic activity compared with Bi2O3. Specifically, the optimal degradation efficiency of AO7 is achieved over the 3R-Bi2O3-x (concentration of NaBH4: 3 mmol/L), which is 1.38 times higher than the degradation AO7 efficiency over Bi2O3. After the decoration of the 3R-Bi2O3-x surface with CQDs, the simulated-sunlight-driven photocatalytic activity of the CQDs/Bi2O3-x composite could be further enhanced. Among the samples, the 15C/3R-Bi2O3-x sample reveals the highest photocatalytic activity, leading to an AO7 degradation percentage of ~97% after 60 min irradiation. Different from Bi2O3 and the 3R-Bi2O3-x, the 15C/3R-Bi2O3-x sample also exhibits near-infrared (NIR)-light-driven photocatalytic degradation activity. In addition, the intrinsic photocatalytic activity of CQDs/Bi2O3-x composite was further confirmed by the degradation of phenol under simulated sunlight and NIR light irradiation. The photocurrent response and electrochemical impedance spectroscopy (EIS) measurements confirm the efficient migration and separation of photogenerated charges in the CQDs/Bi2O3-x samples. The •OH and h+ are proved to be the main reactive species in the simulated sunlight and NIR light photocatalytic processes over the CQDs/Bi2O3-x composites. According to the above experiments, the photocatalytic degradation mechanisms of the CQDs/Bi2O3-x composites under simulated sunlight and NIR light illumination were proposed.

NH3-Sensing Mechanism Using Surface Acoustic Wave Sensor with AlO(OH) Film

In this study, AlO(OH) (boehmite) film was deposited onto a surface acoustic wave (SAW) resonator using a combined sol-gel and spin-coating technology, and prepared and used as a sensitive layer for a high-performance ammonia sensor. The prepared AlO(OH) film has a mesoporous structure and a good affinity to NH₃ (ammonia gas) molecules, and thus can selectively adsorb and react with NH₃. When exposed to ammonia gases, the SAW sensor shows an initial positive response of the frequency shift, and then a slight decrease of the frequency responses. The sensing mechanism of the NH₃ sensor is based on the competition between mass-loading and elastic-loading effects. The sensor operated at room temperature shows a positive response of 1540 Hz to 10 ppm NH₃, with excellent sensitivity, selectivity and stability.

NaBH4-Reduction Induced Evolution of Bi Nanoparticles from BiOCl Nanoplates and Construction of Promising Bi@BiOCl Hybrid Photocatalysts

In this work, we have synthesized BiOCl nanoplates (diameter 140–220 nm, thickness 60–70 nm) via a co-precipitation method, and then created Bi nanoparticles (diameter 35–50 nm) on the surface of BiOCl nanoplates via a NaBH4 reduction method. By varying the NaBH4 concentration and reaction time, the evolution of Bi nanoparticles was systematically investigated. It is demonstrated that with increasing the NaBH4 concentration (at a fixing reaction time of 30 min), BiOCl crystals are gradually reduced into Bi nanoparticles, and pure Bi nanoparticles are formed at 120 mM NaBH4 solution treatment. At low-concentration NaBH4 solutions (e.g., 10 and 30 mM), with increasing the reaction time, BiOCl crystals are partially reduced into Bi nanoparticles, and then the Bi nanoparticles return to form BiOCl crystals. At high-concentration NaBH4 solutions (e.g., 120 mM), BiOCl crystals are reduced to Bi nanoparticles completely with a short reaction time, and further prolong the treatment time leads to the transformation of the Bi nanoparticles into a two-phase mixture of BiOCl and Bi2O3 nanowires. The photodegradation performances of the samples were investigated by choosing rhodamine B (RhB) as the model pollutant and using simulated sunlight as the light source. It is demonstrated that an enhanced photodegradation performance can be achieved for the created Bi@BiOCl hybrid composites with appropriate NaBH4 treatment. The underlying photocatalytic mechanism was systematically investigated and discussed.

Fabrication of ZnO@Ag3PO4 Core-Shell Nanocomposite Arrays as Photoanodes and Their Photoelectric Properties

In this study, we combine the methods of magnetron sputtering, hydrothermal growth, and stepwise deposition to prepare novel ZnO@Ag₃PO₄ core-shell nanocomposite arrays structure. Through scanning electron microscope (SEM) topography test, energy dispersive spectrometer (EDS) element test and X-ray diffractometry (XRD) component test, we characterize the morphology, element distribution and structural characteristics of ZnO@Ag₃PO₄ core-shell nanocomposite arrays structure. At the same time, we test the samples for light reflectance, hydrophilicity and photoelectric performance. We find that after deposition of Ag₃PO₄ on ZnO nanorods, light reflectance decreases. As the time of depositions increases, light reflectance gradually decreases. After the deposition of Ag₃PO₄, the surface of the sample shows super hydrophilicity, which is beneficial for the photoelectric performance test. Through the optical transient response test, we find that the photo-generated current reaches a maximum when a small amount of Ag₃PO₄ is deposited. As the time of depositions of Ag₃PO₄ increases, the photogenerated current gradually decreases. Finally, we conducted an alternating current (AC) impedance test and also verified the correctness of the photocurrent test. Therefore, the structure is expected to be prepared into a photoanode for use in fields such as solar cells.

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.