Advanced Stimuli-Responsive Structure Based on 4D Aerogel and Covalent Organic Frameworks Composite for Rapid Reduction in Tetracycline Pollution

Intelligentization of materials and structures is an important trend. Herein, the stimuli-responsive 4D aerogel is used as a smart substrate for rapid reduction in tetracycline (TC) pollution, in which this smart stimuli-responsive substrate is designated as P4D. Its fourth dimension originates from stimuli-responsive characteristics with time evolution. Meanwhile, the covalent organic frameworks (COFs) composite is constructed by BiPO₄ and triazine-based sp² carbon-conjugated g-C₁₈N₃-COF (COF-1), which is another key aspect of COF-1/BiPO₄@P4D for rapid photocatalytic degradation regarding TC pollution. This emerging smart structure of COFs@P4D can fix programmable temporary state and recover permanent state under thermal or water stimulus without any complicated equipment. Its performance can be tailored by structure, composition, and function. Compared with traditional powder-form photocatalysts, this stimuli-responsive structure provides attractive advantages, such as high permeable framework, self-adaptivity, flexibly customized functional groups, and fast reduction in TC pollution. The predictable development of COFs@P4D could draw much attention for various promising applications in pollution treatment and sensors.

Rational Integration of ZIF-8 and BiPO4 for Energy Storage and Environmental Applications

Environmental pollution and energy storage are among the most pivotal challenges of today's world. The development of multifunctional materials is required to address these challenges. Our study presents the rational design and synthesis of a hybrid material (ZIF-8@BiPO₄) with dual functionality: an outstanding supercapacitor electrode and an excellent photocatalyst. The ZIF-8@BiPO₄ hybrid structure was obtained by conjoining zinc ions and 2-methylimidazole ligands toward BiPO₄ by a one-pot stirring route at room temperature. The ZIF-8@BiPO₄ resulted in considerably higher specific capacitance (Cs) (489 F g^-1 at a scan rate of 5 mV s^-1; 497 F g^-1 at a current density of 1 A g^-1) than that of pure BiPO₄ (358; 443 F g^-1) and ZIF-8 (185; 178 F g^-1) under the same conditions in a three-electrode cell using the 2 M KOH aqueous electrolyte. Afterward, an asymmetric supercapacitor (ASC) device was fabricated with BiPO₄ as the anode and ZIF-8@BiPO₄ as the cathodes, acquiring an outstanding Cs of 255 F g^-1 at a current density of 0.5 A g^-1 with significant cycling stability (81% over 10,000 cycles). Moreover, the ASC has an energy density of 17.5 Wh kg^-1and a power density of 13,695 W kg^-1, which can be considered to be at the borderline between batteries and supercapacitors. The photocatalytic activity of ZIF-8@BiPO₄ was further studied using a methylene blue (MB) dye and sildenafil citrate (SC) drug-active molecules. The degradation of MB was approximately 78% through the photocatalytic reduction after 180 min of UV irradiation. The outstanding characteristics together with the ecofriendly and low-cost preparation make ZIF-8@BiPO₄ appealing for a broad range of applications.

Polymer-coated BiOCl nanosheets for safe and regioselective gastrointestinal X-ray imaging

Bismuth-based compounds are considered to be the best candidates for computed tomography (CT) imaging of gastrointestinal (GI) tract due to high X-ray absorption. Here, we report the introduction of polymer-coated bismuth oxychloride (BiOCl) nanosheets for highly efficient CT imaging in healthy mice and animal with colitis. We demonstrate simple, low cost and fast aqueous synthesis protocol which provides gram-quantity yield of chemically stable BiOCl nanosheets. The developed contrast gives 2.55-fold better CT enhancement compared to conventional contrast with negligible in vivo toxicity. As a major finding we report a regioselective CT imaging of GI tract by using nanoparticles coated with differentially charged polymers. Coating of nanoparticles with a positively charged polymer leads to their fast accumulation in small intestine, while the coating with negatively charged polymers stimulates prolonged stomach retention. We propose that this effect may be explained by a pH-controlled aggregation of nanoparticles in stomach. This feature may become the basis for advancement in clinical diagnosis of entire GI tract.

Synthesis of BiF3 and BiF3-Added Plaster of Paris Composites for Photocatalytic Applications

A BiF3 powder sample was prepared from the purchased Bi2O3 powder via the precipitation route. The photocatalytic performance of the prepared BiF3 powder was compared with the Bi2O3 powder and recognized as superior. The prepared BiF3 powder sample was added in a plaster of Paris (POP) matrix in the proportion of 0%, 1%, 5%, and 10% by wt% to form POP–BiF3(0%), POP–BiF3(1%), POP–BiF3(5%), and POP–BiF3(10%) composite pellets, respectively, and activated the photocatalytic property under the UV–light irradiation,in the POP. In this work, Resazurin (Rz) ink was utilized as an indicator to examine the photocatalytic activity and self-cleaning performance of POP–BiF3(0%), POP–BiF3(1%), POP–BiF3(5%), and POP–BiF3(10%) composite pellets. In addition to the digital photographic method, the UV–visible absorption technique was adopted to quantify the rate of the de-colorization of the Rz ink, which is a direct measure of comparative photocatalytic performance of samples.

Role of thermal decomposition process in the photocatalytic or photoluminescence properties of BiPO4 polymorphs

Thermal decomposition process was used to obtain modified photocatalytic and/or photoluminescence properties of bismuth phosphate polymorphs. The precursor BiPO₄ , 0.7H₂ O was synthesized by a coprecipitation route. The observed polymorphs were the hexagonal P3₁ 21 hydrate phase BiPO₄ , 0.7H₂ O at 25°C, a mix system of hexagonal and monoclinic P2₁ /n phases at 200°C and 400°C, a mix system of monoclinic phases P2₁ /n and P2₁ /m at 600°C, and a unique monoclinic phase P2₁ /m at 900°C. The X-ray diffraction analyses allowed evidencing lattice deformations due to structural defects. The photocatalytic activities in the presence of rhodamine B in aqueous solution were determined using UV light irradiation. The best photocatalytic efficiencies were observed with the mix systems resulting from thermal decomposition at 400 and 600°C. Photoluminescence experiments performed under UV-laser light irradiation revealed unexpected emissions in the green-orange range, with optimal intensities for the mix systems observed at 400°C. The role of structural defects resulting from decomposition process is discussed. PRACTITIONER POINTS: Thermal decomposition is used to introduce structural defects in BiPO₄ polymorphs The BiPO₄ intermediate systems are used to photodegrade rhodamine B Active species trapping experiments are performed Photoluminescence experiments highlight green-orange emissions Structural defects are at the origin of this photoluminescence.

Recent progress on the enhancement of photocatalytic properties of BiPO4 using π-conjugated materials

Semiconductor photocatalysis is regarded as most privileged solution for energy conversion and environmental application. Recently, photocatalysis methods using bismuth-based photocatalysts, such as BiPO₄, have been extensively investigated owing to their superior efficacy regarding organic pollutant degradation and their further mineralization into CO₂ and H₂O. It is well known that BiPO₄ monoclinic phase exhibited better photocatalytic performance compared to Degussa (Evonik) P25 TiO₂ in term of ultraviolet light driven organic pollutants degradation. However, its wide band gap, poor adsorptive performance and large size make BiPO₄ less active under visible light irradiation. However, extensive research works have been conducted in the past with the aim of improving visible light driven BiPO₄ activity by constructing a series of heterostructures, mainly coupled with π-conjugated architecture (e.g., conductive polymer, dye sensitization and carbonaceous materials). However, a critical review of modified BiPO₄ systems using π-conjugated materials has not been published to date. Therefore, this current review article was designed with the aim of presenting a brief current state-of-the-art towards synthesis methods of BiPO₄ in the first section, with an especial focuses onto its crystal-microstructure, optical and photocatalytic properties. Moreover, the most relevant strategies that have been employed to improve its photocatalytic activities are then addressed as the main part of this review. Finally, the last section presents ongoing challenges and perspectives for modified BiPO₄ systems using π-conjugated materials.

Degradation and mechanism of microcystin-LR by PbCrO4 nanorods driven by visible light

This work focuses on the photocatalytic removal of recalcitrant organic pollutants in water treatment. Based on facile precipitation reaction, we fabricated a photocatalyst (PbCrO₄) in single crystals that present evident response to visible light and employed the catalyst in the photocatalytic decomposition of microcystin-LR (MC-LR). In the degradation test using the nanorods with prepared PbCrO₄ photocatalyst, a 100% removal efficiency (27 min reaction) and a kinetics constant of 0.1356 min^-1 were achieved. Such a high performance of PbCrO₄ in photocatalytic conversion of MC-LR was ascribed to its high carrier separation efficiency, positive valence band (VB) position, and good delocalization of VB and conduction band (CB). The test of electron spin-resonance resonance (ESR) demonstrated that excessive free OH radicals were produced during the PbCrO₄ photocatalysis of MC-LR. The density functional theory (DFT) and LC/MS/MS technology were employed to ascertain the intermediates during the MC-LR photocatalytic degradation. The major intermediates were resulted from the attack of hydroxyl radicals to the ADDA side chains of MC-LR structure. This study provides a proof-of-concept strategy to develop effective photocatalysts to efficiently produce OH radicals for the visible-light induced photocatalytic degradation of MC-LR in water.

Facile synthesis of colloidal photoluminescent BiPO4:Ln (Eu,Tb) nanoparticles well-dispersed in polar solvents

Colloidal photoluminescence BiPO₄:Ln (Eu,Tb) nanoparticles well-dispersed in polar solvents have been prepared, which exhibit organic-red and green colours under UV irradiation.

Synthesis and enhanced visible light photocatalytic CO2 reduction of BiPO4–BiOBrxI1−x p–n heterojunctions with adjustable energy band

A series of novel BiPO₄–BiOBr_xI_1−x p–n heterojunctions were successfully prepared by a facile solvothermal method. The morphology, structure and optical properties of photocatalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and ultraviolet visible diffuse reflectance spectroscopy. The visible light photocatalytic activities of BiPO₄–BiOBr_xI_1−x heterojunctions were investigated by photocatalytically reducing CO₂. After 4 hours of irradiation, the 5% BiPO₄–BiOBr_0.75I_0.25 heterojunction showed the highest photocatalytic activity with the yields of CO and CH₄ up to 24.9 and 9.4 μmol g_cat⁻¹ respectively. The improved photocatalytic activity may be due to the formation of BiPO₄–BiOBr_xI_1−x p–n heterojunctions which can effectively restrict the recombination rate of the photoexcited charge carriers. Moreover, the energy band structure of BiPO₄–BiOBr_xI_1−x heterojunctions could be easily adjusted by changing the mole ratio of I and Br. The possible mechanism of the enhancement of the photocatalytic performance was also proposed based on experimental and theoretical analysis. The present study may provide a rational strategy to design highly efficient heterojunctions with an adjustable energy band for environmental treatment and energy conversion.

A series of novel BiPO₄–BiOBr_xI_1−x p–n heterojunctions were successfully prepared by a facile solvothermal method.

Challenges and prospects of advanced oxidation water treatment processes using catalytic nanomaterials

Centralized water treatment has dominated in developed urban areas over the past century, although increasing challenges with this model demand a shift to a more decentralized approach wherein advanced oxidation processes (AOPs) can be appealing treatment options. Efforts to overcome the fundamental obstacles that have thus far limited the practical use of traditional AOPs, such as reducing their chemical and energy input demands, target the utilization of heterogeneous catalysts. Specifically, recent advances in nanotechnology have stimulated extensive research investigating engineered nanomaterial (ENM) applications to AOPs. In this Perspective, we critically evaluate previously studied ENM catalysts and the next-generation treatment technologies they seek to enable. Opportunities for improvement exist at the intersection of materials science and treatment process engineering, as future research should aim to enhance catalyst properties while considering the unique roadblocks to practical ENM implementation in water treatment.

Impacts of ionic liquid capping on the morphology and photocatalytic performance of SbPO4 crystals

A novel hydrothermal route to prepare SbPO₄ with [BMIM][PO₄] or Na₂HPO₄·12H₂O as the phosphorus source has been developed. The morphology transition of SbPO₄ photocatalysts from microparticles to microspheres was shown by changing the reaction temperature.

Integrated BiPO4 nanocrystal/BiOBr heterojunction for sensitive photoelectrochemical sensing of 4-chlorophenol

A sensor platform was constructed by using a BiPO₄ nanocrystal/BiOBr heterojunction, which displayed superior performance for monitoring 4-chlorophenol.

Fabrication of Pt/Cu3(PO4)2 ultrathin nanosheet heterostructure for photoelectrochemical microRNA sensing using novel G-wire-enhanced strategy

Herein, we focus on preparing a highly efficient photocatalytic material to construct a signal-on photoelectrochemical (PEC) sensing platform in view of the rigorous demand of accurate miRNA quantification. The well-dispersed Pt nanoclusters-coated copper phosphate ultrathin nanosheets (PtNCs/Cu₃(PO₄)₂NSs) were first successfully synthesized as a photoelectrode material. Because of the ultrathin two-dimensional lamellar structure of Cu₃(PO₄)₂NSs with a 1.3 nm thickness, as well as the homogeneous size and abundant PtNCs loaded on Cu₃(PO₄)₂NSs, the resultant PtNCs/Cu₃(PO₄)₂NSs were employed as a photoelectrode material for the first time and revealed outstanding photocatalytic activity in PEC sensing as a substrate. As a well-designed protocol, we realized accurate miRNA quantification via a novel signal amplification strategy based on G-wire superstructure exponentially ligating a signal probe, which possesses efficient and simple operation compared to the traditional amplification method. Moreover, the electron donor is generated in situ by lactate oxidase (Lox) labels catalyzing lactate for H₂O₂ production, boosting the efficient separation of electron-hole pairs for further signal amplification. Impressively, this PEC sensing platform is commendably utilized to determine miRNA-141 from prostate carcinoma cell line 22Rv1. This study, considering the excellent PtNCs/Cu₃(PO₄)₂NSs combined with G-wire superstructure for exponential signal amplification strategy, paves a new path in biosensing and clinical diagnosis.

Hierarchical h-, m- and n-BiPO4 microspheres: facile synthesis and application in the photocatalytic decomposition of refractory phenols and benzene

Hierarchical structured n-BiPO₄ microspheres were prepared and exhibited excellent activity for photocatalytic degradation of bisphenol A, phenol, p-chlorophenol and benzene.

Modification with Metallic Bismuth as Efficient Strategy for the Promotion of Photocatalysis: The Case of Bismuth Phosphate

A BiPO4 nanostructure modified with Bi nanoparticles rich in oxygen vacancies in the surface and subsurface was prepared through a one-pot solvothermal treatment utilizing the weak reductive ability of ethylene glycol (EG). The presence of Bi nanocrystals and oxygen vacancies is beneficial for the separation and consumption of photogenerated electrons and holes where Bi nanocrystals act as active sites for the formation of (.) OH and oxygen vacancies are active sites for (.) O2 (-) formation. The enhanced photocatalytic activity is ascribed to the synergistic effect of Bi nanocrystals and surface oxygen vacancies.

A new Bi-based visible-light-sensitive photocatalyst BiLa1.4Ca0.6O4.2: crystal structure, optical property and photocatalytic activity

A new compound of BiLa_1.4Ca_0.6O_4.2 is synthesized through solid state reaction, where the Ca substitutes, in part, the La site in a stable BiLa₂O_4.5 phase. The structure of the BiLa_1.4Ca_0.6O_4.2 crystallizes in space group R3mH with a hexagonal lattice constants of a = 3.893(1) Å, c = 9.891(1) Å. Its optical absorption edge is about 2.05 eV, which just spans the visible light region. The photocatalytic activity of the BiLa_1.4Ca_0.6O_4.2 powder to degradation of RhB under visible light irradiation is measured and improved more than 7 times by annealing in nitrogen ambient, indicating that annealing in nitrogen can effectively improve the photocatalytic activity by producing oxygen vacancy. Although the absolute photocatalytic activity obtained is low, there is great potential for enhancing the activity such as nanoscaling, doping, and coupling with other compounds.

Novel I-BiOBr/BiPO4 heterostructure: synergetic effects of I− ion doping and the electron trapping role of wide-band-gap BiPO4 nanorods

Outstanding activity of I-BiOBr/BiPO₄ was displayed due to the synergetic effects of doped I⁻ ions in I-BiOBr and I-BiOBr/BiPO₄ interface.

In situ growth of Ag3PO4 on N-BiPO4 nanorod: A core-shell heterostructure for high performance photocatalyst

Enhanced light absorption and effective separation of photogenerated charges are the main strategies to improve the performance of photocatalytic materials. In this study, Ag3PO4/N-doped BiPO4 (N-BiPO4) core-shell structure photocatalyst was synthesized by a simple in-situ growth strategy in an organic solvent. The separation of photogenerated electron-hole was enhanced by the doping of nitrogen, because of the emergence of N-O impurity energy levels. The increased photocatalytic activity of Ag3PO4/N-BiPO4 could be attributed to the in-situ formation of chemical bonds between Ag3PO4 and N-BiPO4, which accelerate the separation of electron-hole pairs. The photocatalytic performance of the as-synthesized Ag3PO4/N-BiPO4 was evaluated by monitoring the decolorization of methyl orange under sunlight irradiation. Ag3PO4/N-BiPO4 was capable of bleaching 95% MO within 40min.

A review of BiPO4, a highly efficient oxyacid-type photocatalyst, used for environmental applications

This review presents the recent progress on the oxyacid-type photocatalyst, BiPO₄, which possesses excellent UV-activity for environmental applications.

Synthesis of ionic liquid-modified BiPO4 microspheres with hierarchical flower-like architectures and enhanced photocatalytic activity

Ionic liquid modified onto the surface of BiPO₄ can trap photoexcited electrons and enhance the separation of electron–hole pairs.

Facile preparation of Chevreul's salt (Cu2SO3·CuSO3·2H2O) mesocrystalline microspheres and their high photocatalytic activity

Cu₂SO₃·CuSO₃·2H₂O mesocrystalline microspheres with excellent photocatalytic performance, composed of sub-microparticles in an oriented fashion, are synthesized by a facile method.

AgBr nanoparticles decorated BiPO4 microrod: a novel p–n heterojunction with enhanced photocatalytic activities

AgBr nanoparticles were decorated on the surface of BiPO₄ micro-rod to fabricate a novel p–n heterojunction photocatalyst via a facile deposition–precipitation method.

A novel p–n junction Ag3PO4/BiPO4-based stabilized Pickering emulsion for highly efficient photocatalysis

This study demonstrates a new kind of photocatalytic system via utilization of the superior specific properties inherent in Pickering emulsions.

Facile synthesis of Ag/AgCl/BiPO4 plasmonic photocatalyst with significantly enhanced visible photocatalytic activity and high stability

Highly efficient Ag/AgCl/BiPO₄ plasmonic photocatalyst was synthesized for the first time. The catalyst showed excellent visible photocatalytic activity and high stability. A surface plasmon resonance mechanism was investigated.

Effect of pH on the sonochemical synthesis of BiPO4 nanostructures and its electrochemical properties for pseudocapacitors

Using sonochemical method, BiPO4 nanocrystals were prepared at different pH conditions (pH-1, 3, 5, 7, 9 & 12) for the possible applications of pseudocapacitor electrodes. The prepared BiPO4 nanocrystals belong to monoclinic structure with P21 space group. The SEM image revealed that the particles changed from irregular coarse shape into rod like structure (pH-1 to 7) which finally collapsed into irregular aggregates (pH-9 to pH-12). The observed spot patterns from SAED inferred the polycrystalline nature of the material. The electrochemical performance of the synthesized BiPO4 in various ultrasound irradiation conditions such as irradiation time (30min, 1h, 2h and 3h) and ultrasonication power (40%, 50%, 60% and 70% of instrumental power) was studied. A maximum specific capacitance of 1052F/g (pH-7 at 2mV/s) was observed for the BiPO4 prepared in the ultrasonication reaction condition of 2h with 60% power. Also the obtained specific capacitance was high compared with the conventional precipitation method (623F/g at 2mV/s) that revealed the prominence of sonication method. Similarly, BiPO4 prepared at pH-7 delivered a maximum specific capacitance of 302F/g at 2mA/cm(2) calculated from galvanostatic charge-discharge (GCD) method than the other pH conditions. However, the cycling stability of BiPO4 (pH-7) was not appreciable even for 200 cycles. So, attempts were taken to enhance the cycling stability of the material by employing various carbon matrices such as acetylene black, activated carbon and MWCNT instead of carbon black during electrode preparation. BiPO4 material with activated carbon delivered good capacitance retention compared with other carbon matrices. This enhanced electrochemical performance of BiPO4 (pH-7) using activated carbon matrix inferred that it could be utilized as efficient negative electrode material for pseudocapacitors.

Controllable synthesis of phosphate-modified BiPO4 nanorods with high photocatalytic activity: surface hydroxyl groups concentrations effects

Surface modification by phosphate efficiently improves the photocatalytic performance of BiPO₄ for the degradation of methylene orange (MO), by enhancing the concentration of surface hydroxyl groups and improving its hydrophilicity.