Photocatalytic Enhancement Mechanism Research Articles

Efficient removal of bisphenol A from water using a novel organic–inorganic hybrid heterojunction

Organic-inorganic hybrid heterojunctions have the ability to efficiently remove trace pollutants from water due to efficient photosensitivity. In this work, an organic–inorganic hybrid S-scheme heterojunction photosensitizer (RCP-BW) was successfully fabricated by growing cross-linked β-CD/riboflavin copolymer on the surface of bismuth tungstate (Bi2WO6). The fabrication of the copolymer retains the photosensitivity of riboflavin and the confinement effect of β-CD and forms an internal electric field with Bi2WO6 to enhance the photoelectron transport ability. Photogenerated electrons are transferred and stacked from Bi2WO6 to β-CD/riboflavin copolymers, which greatly enhances the ability of organic copolymers to reduce oxygen and produce superoxide radicals. We combined electrochemistry, free radical chemistry and DFT to study the photoelectron migration mechanism and photocatalytic performance enhancement mechanism in S-scheme heterojunctions. The pseudo-first-order reaction kinetic constant (kRCP-BW = 0.081 min−1) for BPA degradation was four times that of unmodified BW (kBW = 0.020 min−1). β-CD regulates the band structure of riboflavin to match with Bi2WO6, and utilizes charged contaminants and intermediate degradation products to promote the production of reactive oxygen species through interface electron transfer and excited state transition energy transfer. This work provides theoretical support and technical means for photocatalytic oxidation technology to control endocrine disruptors.

From waste to treasure: Synthesis of Ag3PO4/TiO2/r-SiC composite photocatalysts with efficient photocatalytic performance using waste photovoltaic silicon wafers

The conversion of low-value waste into high-value-added photocatalysts for pollution removal is considered a promising approach for waste utilization. In this work, regenerated SiC (r-SiC) nanowires were synthesized using waste photovoltaic silicon wafers through a mechanochemical-carbothermal reduction method. The prepared filamentary structure of r-SiC nanowires as a substrate for an Ag3PO4/TiO2/r-SiC (APO/TIO/r-SiC) ternary photocatalyst was prepared by immobilizing TiO2 and Ag3PO4 on r-SiC nanowires. The 30%APO/TIO/r-SiC (loaded with 30 wt%Ag3PO4) achieved more than 90% degradation rate for six organic dyes, and 80% for tetracycline (TC) within 15 min, respectively. The loading of TiO2 and Ag3PO4 improved the adsorption of molecular oxygen in the aqueous environment, which facilitated the generation of reactive oxygen species and enhanced the photocatalytic performance of 30%APO/TIO/r-SiC. The Z and II dual-scheme electron transfer mechanism for 30%APO/TIO/r-SiC was demonstrated to promote effectively carrier separation. Three potential pathways of RhB degradation were proposed, and the disruption of the conjugated structure (chromophore) was the main cause of RhB degradation. The radical quenching experiments revealed that the degradation process was more significantly influenced by •O2- and •OH than h+. The research proposed a promising 'win-win' treatment approach for waste photovoltaic wafers and delved into the photocatalytic performance and enhancement mechanism of SiC-based composite catalysts.

Construction of ternary CN/Ag/P25 photocatalysts for naphthalene photodegradation

Ternary CN/Ag/P25 photocatalysts are successfully constructed are successfully constructed by photodeposition method and their photodegradation performances of naphthalene are evaluated. The results show the sample prepared by depositing 1 % nano-Ag particles onto the photocatalyst exhibits the best activity towards naphthalene photodegradation with satisfactory stability. The structures, morphologies and optical properties of the obtained photocatalysts are characterized by various analytical methods and the possible photocatalytic enhancement mechanism is proposed. •O2– and h+ play key roles in the process of naphthalene photodegradation. Nano-Ag particles work as electron-conduction bridges, facilitating the migration of charge carriers and providing electrons for O2 to produce •O2– radicals for naphthalene photodegradation. Meanwhile, the recombination of e--h+ is inhibited, resulting in the accumulation of h+. In general, the successful construction of ternary CN/Ag/P25 photocatalysts provides a new strategy to design novel photocatalysts for naphthalene photodegradation.

Enhancing Photocatalysis: Understanding the Mechanistic Diversity in Photocatalysts Modified with Single-Atom Catalytic Sites.

Surface modification of heterogeneous photocatalysts with single-atom catalysts (SACs) is an attractive approach for achieving enhanced photocatalytic performance. However, there is limited knowledge of the mechanism of photocatalytic enhancement in SAC-modified photocatalysts, which makes the rational design of high-performance SAC-based photocatalysts challenging. Herein, a series of photocatalysts for the aerobic degradation of pollutants based on anatase TiO2 modified with various low-cost, non-noble SACs (vanadate, Cu, and Fe ions) is reported. The most active SAC-modified photocatalysts outperform TiO2 modified with the corresponding metal oxide nanoparticles and state-of-the-art benchmark photocatalysts such as platinized TiO2 and commercial P25 powders. A combination of in situ electron paramagnetic resonance spectroscopy and theoretical calculations reveal that the best-performing photocatalysts modified with Cu(II) and vanadate SACs exhibit significant differences in the mechanism of activity enhancement, particularly with respect to the rate of oxygen reduction. The superior performance of vanadate SAC-modified TiO2 is found to be related to the shallow character of the SAC-induced intragap states, which allows for both the effective extraction of photogenerated electrons and fast catalytic turnover in the reduction of dioxygen, which translates directly into diminished recombination. These results provide essential guidelines for developing efficient SAC-based photocatalysts.

Sorghum straw carbon assisted preparation of thin-sheet like BiOCl with boosted photocatalytic activity toward detoxification of three contaminants

In this work, a one-pot hydrothermal method was employed to fabricate sorghum straw carbon (SSC) modified BiOCl catalysts. SSC not only operates as a template agent to regulate the microscopic morphology of BiOCl to form thinner lamellar structures but also constructs oxygen vacancies (OVs), which together enhance the photocatalytic ability. The samples were researched by Brunauer-Emmett-Teller (BET), X-ray diffractometer (XRD) and scanning electron microscope (SEM). Addition of SSC induce BiOCl to form a flower spherical-like structure assembled by thin sheets. Surface photovoltage spectroscopy (SPS) and electrochemical experiments confirm that the dense interlayer stacking provides more pathways for the separation of charges from bulk to the surface, and the thinner sheet thickness shortens the separation time for the charges, boosting the activity of the photocatalysts. The existence of the main reactive radicals (O2– and h+) in the photocatalytic system was investigated by trapping experiments. Photocatalytic activity of the samples was assessed by destruction of rhodamine B (RhB), tetracycline (TC) and perfluorooctanoic acid (PFOA). When the mass ratio of SSC/BiOCl is 0.75%, the catalyst shows the best photocatalytic activity. A reasonable photocatalytic enhancement mechanism was proposed in combination with the observation results.

Magnetic CoFe1.95Y0.05O4-Decorated Ag3PO4 as Superior and Recyclable Photocatalyst for Dye Degradation.

The Ag3PO4/CoFe1.95Y0.05O4 nanocomposite with magnetic properties was simply synthesized by the hydrothermal method. The structure and morphology of the prepared material were characterized, and its photocatalytic activity for degradation of the methylene blue and rhodamine B dyes was also tested. It was revealed that the Ag3PO4 in the nanocomposite exhibited a smaller size and higher efficiency in degrading dyes than the individually synthesized Ag3PO4 when exposed to light. Furthermore, the magnetic properties of CoFe1.95Y0.05O4 enabled the nanocomposite to possess magnetic separation capabilities. The stable crystal structure and effective degradation ability of the nanocomposite were demonstrated through cyclic degradation experiments. It was shown that Ag3PO4/CoFe1.95Y0.05O4-0.2 could deliver the highest activity and stability in degrading the dyes, and 98% of the dyes could be reduced within 30 min. Additionally, the photocatalytic enhancement mechanism and cyclic degradation stability of the magnetic nanocomposites were also proposed.

Synergistic effects of cocatalyst and homojunction/heterojunction with boosted photocatalytic H2 evolution over Zn0.5Cd0.5S/NDs

For improved photocatalytic hydrogen evolution, building heterojunction structures has been considered as a promising strategy to promote charge separation and transportation. Herein, an in-situ hydrothermal process was used to prepare the novel twin Zn0.5Cd0.5S/NDs (ZCND-x) homojunction/heterojunction photocatalyst of nanodiamonds (NDs) dots anchored twin Zn0.5Cd0.5S (T-ZCS). Among all the composites, the ZCND-10 hybrid exhibits a much higher H2 performance of 160.035 mmol/g/h with a mixture of Na2S and Na2SO3 (pH = 13.82) as hole eliminator agent, which is considerably 5.3 times that of pure T-ZCS nanoparticles. Furthermore, the optimum apparent quantum yield (AQY) of ZCND-10 is up to 32.42% at λ = 420 ± 15 nm. At the same time, ZNCD-10 heterojunction owns excellent H2 evolution cycle activity and photostability. Simultaneously, photocatalyst depicts good photocatalytic overall water splitting performance. Meanwhile, experimental characterization results indicate extend light response, high surface area, as well as accelerate charge separation of homojunction/heterojunction induced phase junctions by the interfacial synergistic effect between T-ZCS and NDs, endowed with excellent H2 evolution performance and chemical stability. Theoretical work functions, electron density distribution and in-situ XPS further clarify the electron transfer pathway between T-ZCS and NDs. The potential mechanism of photocatalytic enhancement of ZCND-x hybrid is proposed, which may lead to a new thinking for the efficient preparation of other photocatalytic materials.

Novel incomplete phase transition from α-Bi2O3 to γ-Bi2O3 constructing dual interfaces contacts with BaTiO3 for highly efficient degradation of antibiotics

Incomplete lattice transition in heterojunction preparation can generate another crystal phase to provide a new transfer channel of electrons and holes for enhancing photocatalytic activity. In this paper, the hydrothermal synthesis of BaTiO3 and α-Bi2O3 composite induced a part of α-Bi2O3 to γ-Bi2O3 lattice transition. Except for α-Bi2O3/BaTiO3 interface, a new BaTiO3/γ-Bi2O3 contact was formed to realize another transfer channel of the charge carriers. The removal efficiencies of norfloxacin and lomefloxacin using the optimal α-Bi2O3/BaTiO3/γ-Bi2O3 sample reached 93% and 95%, much higher than those of the pure phases and the diphasic heterojunction samples. After five times of cycle tests, the photodegradation efficiencies of these two antibiotics were above 90% and 91%, respectively, while the crystal structure of the sample unchanged to exhibit good structure stability. The superoxide radical (O2−), hole, and hydroxyl radicals (OH−) were the main active substances upon the antibiotics degradation. The photocatalytic enhancement mechanism was originated from the formation of a new Z-type energy band according to the surface and interface calculation. Finally, the analysis of mass spectrometry revealed the degradation processes of these two pollutants. These results provided a simple way to obtain efficient double interfaces heterojunction photocatalysts for removing antibiotic pollutants.

G-C3N4-Loaded Carbon Nanofiber for Efficient Photocatalytic Hydrogen Production

g-C3N4-loaded carbon nanofibers (CNCNF) were obtained via electrostatic spinning and high temperature calcination. Highly crystalline g-C3N4 can be obtained at 800 °C due to the protection of carbon nanofibers. Benefiting from the high conductivity of carbon nanofibers and the high carrier separation efficiency of g-C3N4, CNCNF shows a significantly enhanced photocatalytic hydrogen production activity (7.7-fold more than pristine g-C3N4), also, the mechanism of photocatalytic performance enhancement is discussed.

In-situ construction of h-BN/BiOCl heterojunctions with rich oxygen vacancies for rapid photocatalytic removal of typical contaminants

BiOCl -based semiconductors have caused considerable concern in photocatalytic field to solve environmental problems because of their special layered structure. To improve the utilization of sunlight by BiOCl and inhibit the high recombination rate of photo-induced charge pairs, forming of heterojunction is a valuable approach to settle these issues. Hexagonal boron nitride (h-BN) is a suitable semiconductor that can match the band structure of BiOCl. Therefore, in this demonstration, h-BN/BiOCl heterojunctions were constructed via a solvothermal strategy. Introduction of oxygen vacancies (OVs) in the heterojunctions increases the effective separation of photo-generated charge pairs and reduces the energy required for electrons to reach a new energy level constructed by OVs. The photocatalytic properties of catalysts were investigated by disintegration of rhodamine B (RhB), tetracycline (TC) and perfluorooctanoic acid (PFOA) used as simulated pollutants in photocatalytic experiments. The best photocatalytic performance was obtained when the mass ratio of h-BN to BiOCl is 1% and the photocatalysts have fine stability. Combining all the results, photocatalytic enhancement mechanism was reasonably elucidated.

SrTiO3 nanosheets decorated with ZnFe2O4 nanoparticles as Z-scheme photocatalysts for highly efficient photocatalytic degradation and CO2 conversion

Nanocomposite has attracted widespread attention for efficiently utilizing solar energy and improving conversion efficiency during wastewater purification and solar fuels evolution. In this study, Z-scheme ZnFe2O4-SrTiO3 nanocomposite was prepared and used as photocatalysts for tetracycline hydrochloride (TCH) degradation and CO2 conversion. The as-obtained ZnFe2O4-SrTiO3 system achieved drastically enhanced TCH degradation efficiency up to 84.56 % with respect to pure ZnFe2O4(13.81 %) and SrTiO3(49.66 %) under visible light irradiation. The influences of ZnFe2O4 content and co-existing ions on the photodegradation activities were investigated. In addition, ZnFe2O4-SrTiO3 nanocomposite exhibited outstanding CO2 photoreduction activity, the CO and CH4 evolution rate were 8.24 μmol/g/h and 2.51 μmol/g/h, which was 2.5 and 6.4 times higher than that observed for SrTiO3, respectively. The reinforced photocatalytic TCH degradation and CO2 conversion activities are mainly attributed to the obviously enhanced utilization of solar energy and the dramatically boosted electron-hole pair separation efficiency through a Z-scheme charge transfer model. In addition, a possible photocatalytic enhancement mechanism of ZnFe2O4-SrTiO3 nanocomposite is proposed in the light of trapping experiments, ESR and DFT calculations. Our studies implies that ZnFe2O4-SrTiO3 nanocomposite are expected to effectively realize wastewater purification and CO2 reduction to renewable solar fuels.

Uncovering mechanism of photocatalytic performance enhancement induced by multivariate defects on SnS2

Uncovering mechanism of photocatalytic performance enhancement induced by multivariate defects on SnS2

Panax notoginseng powder -assisted preparation of carbon-quantum-dots/BiOCl with enriched oxygen vacancies and boosted photocatalytic performance

Low activity of photocatalysts is a serious bottleneck to the practical application of photocatalytic technology. In this paper, a series of BiOCl composite photocatalysts containing carbon quantum dots (CQDs) were successfully prepared by adding Panax notoginseng powder (PNP) to the solvothermal synthesis system of BiOCl as a template agent and a raw material for 0D CQDs. CQDs/BiOCl exhibit 2D flake structures and 3D flower-like microspheres self-assembled from thin flakes, holding rich oxygen vacancies (OVs). After detailed characterization, it was found that the amount of OVs on BiOCl could be regulated according to the amount of PNP added. The CQDs/OVs-BiOCl photocatalysts exhibit higher photogenerated charge separation efficiency and photocatalytic activity than the bare BiOCl. When the mass ratio of PNP/BiOCl is 1.0%, the photocatalyst demonstrates the maximum degradation activity for rhodamine B (RhB) and perfluorooctanoic acid (PFOA). In view of the solid observations, a photocatalytic enhancement mechanism of CQDs/BiOCl was elucidated.

In-situ synthesis of 3D BiOBr/UiO-66-NH2 heterojunction nanocomposite and its excellent photocatalytic degradation of rhodamine B dye

As a primary goal, The fast recombination of stimulated excitons and poor visible light response are key problems in the photocatalysis field. Combining with materials with good visible light responses to form heterogeneous structures is still the most effective way. In this study, BiOBr/UiO-66-NH2 photocatalyst was synthesized by a simple method. BiOBr is a 3D spherical structure stacked by nanosheets, which enhance its adsorption capacity for pollutants and catalyze the dark reaction to reach the equilibrium point for too long. Coupling with UiO-66-NH2, its adsorption capacity was inhibited and the dark reaction time was shortened. The excellent removal rate of Rhodamine B (RhB) by BiOBr/UiO-66-NH2 reached 96.79% after 30 min of visible light irradiation and 99.37% after 90 min. With an increase in pollutant concentration, the composite still showed excellent photocatalytic performance. This study also tried to abandon the dark adsorption stage and directly degraded RhB efficiently and quickly under visible light. Finally, the photocatalytic enhancement mechanism was proposed.

Photodeposition Synthesis of CdS@Ni2P Composites for Efficacious Photocatalytic Hydrogen Evolution

Noble-metal-free semiconductor composites are very valuable for efficient water splitting driven by visible light. In this paper, CdS@Ni2P was successfully prepared by a simple hydrothermal method followed by in situ photodeposition. The results showed that the best photocatalytic hydrogen production rate of the composite is 287 μmol h–1, which is about 98.3 times that of pure CdS. The high activity of the material may be attributed to the intimate interface between the Ni2P cocatalyst and CdS nanorods for accelerating the separation and transport of photoelectrons. Further UV and PL tests found that Ni2P significantly extends the lifetime of photogenerated charge carriers and reduces charge recombination rates, resulting in improved photocatalytic H2 production performance. The potential mechanism of photocatalytic enhancement of CdS@Ni2P composite samples was proposed based on the experimental results and DFT calculation, which could lead to a neoteric approach for the efficient preparation of other photocatalytic materials.

Enhanced visible-light harvesting of triazine-based covalent organic frameworks by incorporating FeⅢ-tannic acid complexes for high-efficiency photocatalysis

Triazine-based covalent organic frameworks (COFs) have recently emerged as a new class of photocatalysts for visible-light-driven photocatalytic reactions. However, the optical absorption edge of triazine-based COFs is usually below 550 nm, resulting in inefficient photocatalytic performance. Herein, a novel FeⅢ-tannic acid (FeⅢ-TA) complexes evenly coating a triazine-based COF (FeⅢ-TA@TTB-TTA) was prepared using a simple self-assembly process. The FeⅢ-TA significantly enhanced the optical absorption of TTB-TTA, especially in the λ > 600 nm region. Consequently, the composite photocatalyst exhibited a higher photodegradation rate of methyl orange (MO), corresponding to a 14-fold enhancement, compared with the bare TTB-TTA. Moreover, the degradation rate was 372 times higher under >600 nm light illumination, indicating that the photocatalytic enhancement mechanism primarily came from the enhanced visible-light harvesting capacity of FeⅢ-TA. This work offers a promising avenue for enhancing the visible-light absorption of triazine-based COFs and providing insights into the research of high-performance photocatalysts.

P123-assisted hydrothermal synthesis of Ag2MoO4 with enhanced photocatalytic performance

To improve photocatalytic activity of Ag2MoO4, in this study, Ag2MoO4 photocatalyst was successfully prepared by a hydrothermal method assisted with EO20PO70EO20 (P123). The prepared Ag2MoO4 photocatalyst (P123-Ag2MoO4) was characterized by some typical analytical methods. The results show that P123-assisted preparation can boost the specific surface area of Ag2MoO4, promote the introduction of oxygen vacancies (OVs) in Ag2MoO4, and accelerate the separation of photoinduced carriers and facilitate the generation of O2–, therefore improving the photocatalytic activity of Ag2MoO4. Under UV light irradiation, catalytic performance of the photocatalysts was evaluated by degradation of methyl orange (MO). When the mass ratio of P123/Ag2MoO4 is 4%, the photocatalytic activity of Ag2MoO4 is 10.1 times higher than that of the blank Ag2MoO4. Considering the results, photocatalytic enhancement mechanism was elaborated. This study provides a facile and effective preparation method to boost the photocatalytic activity of Ag2MoO4 photocatalyst.

Photocatalytic property of MWCNTs/BiOI with rich oxygen vacancies

In this paper, BiOI was surface decorated by multiwall carbon nanotubes (MWCNTs) via a hydrothermal method. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscope (HRTEM), UV–Vis diffusion reflectance spectrometry (DRS), X-ray photoelectron spectroscopy (XPS), surface photovoltage spectroscopy (SPS), and electron spin-resonance (ESR). Rich oxygen vacancies (OVs) were generated on the surface of BiOI, confirmed by ESR and XPS characterization. Trapping tests prove that superoxide (•O2−) is the key active species. When the mass ratio of MWCNTs/BiOI is 1.0%, the photocatalytic activity of MWCNTs/BiOI is 5.6 times of that of the bare BiOI. Finally, photocatalytic enhancement mechanism was proposed based on the experimental consequences. After surface modification by MWCNTs, electrons will transfer to MWCNTs due to the strong interaction between MWCNTs and BiOI, and the excellent conductivity of MWCNTs, significantly boosting the separation of e−/h+ pairs.

Photocatalytic performance of rich OVs-BiOCl modified by polyphenylene sulfide

Introduction of oxygen vacancies (OVs) on the surface of photocatalyst has been proved to be a potent avenue to improve photocatalytic capability by accelerating the segregation of photoactivated carriers and creating a defect energy level. In this presentation, a facile hydrothermal approach was performed to fabricate polyphenylene sulfide (PPS)/OVs-BiOCl composites to further improve the catalytic capability of OVs enriched BiOCl. The successful construction of rich OVs in BiOCl was firmly confirmed by X-ray photoelectron spectroscopy (XPS) and low- temperature electron spin resonance (ESR). Surface photovoltage spectrum (SPS) and electrochemical characterization display that the existence of PPS in the synthetic system dramatically affects the surface states of BiOCl, expediting the segregation of photoinduced carriers. Photocatalytic capacity of PPS/OVs-BiOCl was examined by disintegration of perfluorooctanoic acid (PFOA), rhodamine B (RhB) and tetracycline (TC). PPS surface modification can significantly improve the photoactivity of OVs-BiOCl toward destruction of PFOA, RhB and TC. Interestingly, when mass ratio of PPS/BiOCl is 0.5%, the degradation capacity of PPS/OVs-BiOCl for decontamination of RhB and TC is 4.25 and 3.10 -fold higher than that of OVs-BiOCl, respectively. In consideration of the observations, the photocatalytic enhancement mechanism for PPS/OVs-BiOCl was elaborated.

Application of a novel biomimetic double-ligand zirconium-based metal organic framework in environmental restoration and energy conversion

The development of visible-light response photocatalysts with a high catalytic performance and long-term cyclic stability is of great significance in the field of energy and environmental protection. Inspired by photosynthesis, a novel three-dimensional coral zirconium-based metal organic framework (MOF) was synthesized using a double-ligand strategy. The optimal sample, Zr-TCPP-bpydc (2:1), (the ratio of tetra-(4-carboxyphenyl) porphyrin to 2,2′-bipyridine-5,5′-dicarboxylic acid is 2:1) shows an excellent photocatalytic activity under visible light irradiation, and the effects of the amount of photocatalyst, pH and concentration on the degradation rate were investigated under the optimum conditions. It has a high degradation rate of tetracycline (98.12% for tetracycline and 96.74% for ofloxacin), which is 2.11 times higher than that of single ligand Zr-bpydc (zirconium-based MOF containing only 2,2′-bipyridine-5,5′-dicarboxylic acid). More importantly, it also has a good H2 evolution rate (213.68 μmol g−1h−1) and CO2 reduction (35.81 μmol g−1h−1). In addition, the intermediate pathway of degradation, photocatalytic enhancement mechanism and cycle stability were deeply studied by liquid chromatography-mass spectrometry (LC-MS), electron spin resonance spectroscopy (ESR), linear sweep voltammetry (LSV) and recycling tests. The synthesis of a three-dimensional biomimetic coral zirconium-based MOF material will provide guidance for the development of new, promising, and natural ideal photocatalytic materials.