Transfer Of Photogenerated Electrons Research Articles

Au/Ti3C2/g-C3N4 Ternary Composites Boost H2 Evolution Efficiently with Remarkable Long-Term Stability by Synergistic Strategies.

The use of novel two-dimensional MXene materials and conventional g-C3N4 photocatalysts to fabricate the composites for hydrogen evolution reaction (HER) has attracted much attention, for which there is plenty of room for the enhancement of hydrogen evolution rates particularly under visible light and photostability. Herein, g-C3N4 was modified by copolymerization of malonamide and melamine and used to fabricate the ternary composites of Au particles and Ti3C2 MXene, and based on the synergistic effect, the composites enhanced the hydrogen evolution rates by 2.1, 99.8, and ∞ times compared with the unmodified g-C3N4 under UV, simulated sunlight, and visible light illumination, respectively. Moreover, the composite exhibited a sustained hydrogen evolution capacity in the cycle test for up to 120 h. Theoretical calculations and experimental results indicated that the hot electrons of Au are injected into the modified g-C3N4 and transferred to Ti3C2 simultaneously along with the photogenerated electrons of the modified g-C3N4 and then further transferred to Au, forming a photogenerated electron transfer channel of Au and modified g-C3N4 → Ti3C2 → Au within the composite. Ti3C2 acts as a bridge for fast separation of photogenerated electrons and holes on Au and modified g-C3N4, playing a key role in the enhanced photocatalytic performance. In addition, the visible light absorption ability of Au also positively contributed to the enhancement of visible light photocatalytic performance by providing hot electrons. Therefore, the selection of suitable cocatalysts for the design of composites is a crucial research direction to improve the photocatalytic performance and photostability of photocatalysts.

Porphyrin-functionalized non-magnetic steel slag as bifunctional nanozymes for colorimetric detection and photocatalytic degradation of tetracycline

Inspired by natural enzymes with various activities, controlling the catalytic activity of nanozymes through suitable strategies has received extensive attention. By modifying non-magnetic steel slag material (NMSS) with porphyrin, we developed a new kind of bifunctional nanozymes (NMSS-Por) with both simulated enzyme activity and photocatalytic activity. The NMSS-Por nanozymes exhibit outstanding colorimetric sensing and photodegradation performances, with a limit of detection (LOD) of 0.257 µM, 0.102 µM and 0.142 µM for tetracycline (TC), oxytetracycline, and doxycycline, while a removal rate of 79 % for TC after 60 min. Hydroxyl radical (·OH), positively charged hole (h+), singlet oxygen (1O2), and photogenerated electron transfer process play vital roles in both catalytic reactions. Besides, NMSS-Por nanozymes has excellent selectivity for TC detection and can also be used as promising photocatalysts for real water treatment. This work provides a new and promising strategy for the high value-added resource utilization of waste steel slag in environmental catalysis, which is in accordance with the sustainable development of green chemistry.

Nickel-doped microtubular CeVO4 inspired by wood powder structure for visible light photocatalytic degradation of methylene blue and bacterial inactivation

In this study, inspired by natural wood powder structure, nickel-doped microtubular cerium vanadate (Ni/T-CeVO4) was obtained using wood powder as a biological template. Photocatalytic experiments under visible light revealed that Ni/T-CeVO4-3wt possessed the highest photocatalytic activity, with a degradation efficiency of up to 99 % for methylene blue. The enhanced photocatalytic performance was not only attributed to the microtubule wood powder structure assigned the composite a larger specific surface area but also the nickel doping narrowed the band gap of the composites while introducing more oxygen vacancies. The rapidly generated current in transient photocurrent responses and small arc radius in electrochemical impedance spectra further indicated the higher photogenerated carrier separation and smaller photogenerated electron transfer resistance within the composite. ESR spin-trapping tests proved that O2− and OH dominated the photocatalytic process. Furthermore, owing to its unique structural characteristics, the composite showed excellent photocatalytic antibacterial activity against Staphylococcus aureus and Escherichia coli. The present study provides a theoretical basis for developing efficient dual-effect photocatalysts using visible light to remove organic dyes and pathogenic bacteria from the water environment.

Potassium and chlorine co-tuned graphitic carbon nitride for organic pollutants photodegradation: Revealing the effects of cyano groups on O2 evolution

The insufficient active sites and sluggish photogenerated electron migration are hindered the photocatalytic activity of g-C3N4. Herein, we successfully synthesized a K and Cl co-tuned g-C3N4, with cyano groups incorporating (expressed as CN-KCl). The optoelectronic and physicochemical properties of the samples were comprehensively investigated using a combination of characterization techniques and DFT calculations. The results demonstrated that Cl atom replaced sp2-hybridized nitrogen atom, while K atom was doped at the interstitial site. With the synergistic effect of K/Cl atoms, the transfer of photogenerated electrons across layers and lamellae was enhanced. Additionally, the cyano groups not only acted as the most stable adsorption sites for O2, but also served as charge transfer bridge between catalysts and O2, enhancing the activation of O2. This ultimately led to an improvement in the generation of superoxide radicals and contributed to the enhanced photocatalytic activity of CN-KCl.

In-situ FT-IR study of alcohols degradation in the gas phase using different TiO2 composites

Herein, we present an in-situ FT-IR study analysing the interactions and photocatalytic degradation of 1-butanol and methanol in the gas phase through the catalysts Hombikat-b (commercial) and EST-1023 (synthesised in lab), as well as composites of them in a range of pH between 5 and 9. Composite Homb@EST at neutral pH (Homb@EST-pH7) has presented a photocatalytic efficiency much higher than that of the separate catalysts in both the degradation of alcohols and carboxylates. Characterisation analyses have shown that EST-1023 exhibits low surface area and surface hydroxylation, which suggests practically no adsorption of alcohols at the initial stages of the process. Notwithstanding, we have determined a large concentration of surface electronic traps in EST-1023. On the contrary, Hombikat-b presents high surface area and surface hydroxylation, leading to high adsorption rates of the studied alcohols. Aggregate distribution, SEM, and HR-TEM studies have shown that neutral pH is the most appropriate condition to aggregate both catalysts, generating the so-called composite Homb@EST-pH7. The high photocatalytic capability of this composite is attributed to the transfer of photogenerated electrons from the Hombikat-b nanoparticles to the electron traps present in EST-1023, which implies a decrease in the recombination speed of the photogenerated electron-hole (e–/h+) pairs.

Bi2O3@MoS2 heterojunction for enhanced photoelectrocatalytic hydrogen evolution

A Z-type Bi2O3@MoS2 heterojunction was successfully synthesized using a hydrothermal method. Bi2O3 microflowers served as a growth support for MoS2. The Bi2O3@MoS2-10 heterojunction demonstrated optimal photoelectrocatalytic performance as a result of adjusting the loading of MoS2. It exhibited excellent electrocatalytic hydrogen evolution performance, with an overpotential of only 223 mV vs. RHE. This value is approximately half that of pure MoS2 and one-third of Bi2O3. Under illumination, the overpotential for the hydrogen evolution reaction of the Bi2O3@MoS2-10 heterojunction decreased by ∼ 35 mV when the current density reached −10 mA cm−2, compared to dark conditions. The improved performance can be attributed to the growth of MoS2 on the Bi2O3 support, which prevents the aggregation of MoS2 nanosheets and results in a layered structure with a large surface area. Furthermore, the introduction of Bi2O3 as a co-catalyst lowers the bandgap energy of the heterojunction, facilitating efficient separation and rapid transfer of photogenerated electrons and holes. As a result, this growth induces band bending near the heterojunction interface, leading to the rearrangement of energy levels and the redistribution of charges through the interaction between Bi2O3 and MoS2. Moreover, photogenerated electrons can efficiently transfer to the heterojunction surface, participating in the reduction of H+/H3O+ ions to produce H2. This enhances the photoelectrocatalytic hydrogen evolution performance of the Bi2O3@MoS2-10 heterojunction.

Directional and rapid electron transfer in perylene diimide modified iron-manganese bimetallic metal-organic frameworks for enhanced photo-Fenton process

Bimetallic metal-organic frameworks (MOFs) with iron and another transition metal in the inorganic nodes, as newly developed photo-Fenton catalysts, have gained an ample attention because of the synergistic effect and enhanced properties compared to the monometallic counterparts. However, the photo-Fenton application of bimetallic MOFs still faces the obstacle of unsatisfactory photogenerated electrons transfer due to the fast recombination of photogenerated electron-hole pairs. In this work, perylene diimide (PDI) was modified upon bimetallic NH2-MIL-88B(Fe, Mn) (FM88B) via the ammonolysis process to construct PDI/FM88B heterojunction structure. The constructed heterostructure mediated the directional transfer of photogenerated electrons from PDI (electron donor) to FM88 (electron acceptor). The built-in electric field (BIEF) between PDI and FM88B promoted the separation and directional transfer of photogenerated electron-hole pairs. The interfacial amide bond as the high-speed electronic transmission channel reduced the transfer distance and energy barrier of photogenerated electrons from PDI to FM88B, accelerating the photogenerated electrons delivery. As a result, both Fe(III)/Fe(II) and Mn(III)/Mn(II) redox couples were continuously and rapidly cycled, ultimately boosting the performance of FM88B for H2O2 activation. Compared with FM88B, the optimal 6%PDI/FM88B exhibited excellent degradation performance against tetracycline (TC) (degradation efficiency and apparent rate constant, as 89% and 0.067 min−1) and notable synergy between photocatalysis and Fenton-like process (synergistic factor of 77.61%). DFT calculation and HPLC-MS analysis were used to verify the possible degradation pathways of TC. Meanwhile, the corresponding toxicity changes during TC degradation were studied in detail. This work paves the way for improving the heterogeneous photo-Fenton performance of the bimetallic MOFs in environmental remediation.

Immobilizing Triphenylamine with Photoredox Inert Sr2+ Forming Sr‐MOF with Controlled Electron Migration for Photocatalytic Oxidation of Thiols to Disulfides

Comprehensive SummaryThe photocatalytic oxidative coupling of thiols is one of the most popular methods to synthesize the disulfides. Triphenylamine and its derivatives (TPAs) are promising for the above reaction, but suffer from the easy polymerization and difficult separation. To overcome these obstacles while controlling the photogenerated electrons transfer directly to target substrates, herein, we constructed one TPA‐based metal‐organic framework (MOF), (Me2NH2)[Sr(TCBPA)]·DMA·3H2O (1), by direct self‐assembly of tris(4′‐carboxybiphenyl)amine (H3TCBPA) and photoredox inert strontium ion (Sr2+). DFT calculations revealed that the valence band maximum (VBM) and the conduction band minimum (CBM) are mainly located on TCBPA3–, successfully inhibiting the undesirable electron migration to metal nodes. Experimental results indicated that 1 displays superior performance than homogeneous H3TCBPA, which may result from the abundant π···π and C—H···π interactions between the well‐arranged TCBPA3– and the build‐in electric field between the anionic framework and the Me2NH2+. This work highlights that immobilizing TPAs into MOFs is one promising approach to designing heterogeneous photocatalysts for the synthesis of disulfides by oxidative coupling of thiols.

Enhanced photodynamic therapy efficacy of Ni-doped/oxygen vacancy double-defect Ni-ZnO@C photosensitizer in bacteria-infected wounds based on ROS damage and ATP synthesis inhibition

The use of zinc oxide (ZnO) photosensitizers (PSs)-mediated photodynamic therapy (PDT) against bacterial wound infections is greatly restricted by diminished photocatalytic efficiency caused by the rapid recombination of photogenerated electrons and holes. In this work, ZnO PSs with a Ni-doped/oxygen vacancy and a protective carbon shell were successfully synthesized by calcinating a Ni-doping zeolitic imidazolate framework-8 precursor. The double-defect structure and the carbon-based substrates significantly promoted the efficiency of photogenerated electron–hole pair separation, meanwhile, the 3 % Ni doping endows it with great photocatalytic performance as elucidated by photodegradation assays of methylene blue (MB) and density functional theory (DFT) calculations, reinforcing the generation of reactive oxygen species (ROS) by ZnO and showing obvious advantages in antibacterial properties. As the enhanced photogenerated electron transfer and the ROS damage underwent localized accumulation, the PSs disturbed the bacterial membrane integrity and caused bacterial ATP synthesis inhibition, further leading to bacterial lysis and promoting bacterial deaths. Additionally, the PSs showed outstanding efficacy in eradicating bacterial biofilms. Simultaneously, the significantly enhanced PDT antibacterial performance of the PSs in vivo could initiate wound tissue repair and trigger anti-inflammatory reactions by significantly regulating the expression levels of regeneration- and inflammation-related genes or proteins. Furthermore, the PSs consistently exhibited favorable compatibility both in vitro and in vivo. In summary, this study offers evidence of the remarkably efficient and biologically safe performance of Ni-ZnO@C PSs, with antibacterial properties advancing wound healing, both in controlled laboratory environments and living organisms, further underscoring their substantial potential for biomedical applications.

Zn–N bonds boost interfacial charge transfer in ZnO/Nitrogen-Doped porous carbon Schottky heterojunction for enhanced photocatalytic sterilization

Although heterogeneous photocatalytic sterilization can avoid secondary pollution and achieve broad spectrum antibacterial effects, its low disinfection efficiency seriously hinders its development. Exploring and achieving precise electron-transfer channels in the interface of heterogeneous systems are an effective method to enhance photocatalytic sterilization. Herein, we designed a chemical Zn–N bonded nitrogen-doped porous carbon-loaded zinc oxide (ZnO/NC) Schottky heterojunction photocatalyst through oxidizing and carbonizing ZIF-8 in-situ at suitable temperatures. The Zn–N accurately facilitated the photogenerated electrons transfer from the conduction band (CB) site of ZnO to the NC surface as active site. Furthermore, the NC as carrier enhanced the light-absorption capacity (746 nm) of Schottky heterojunction and functioned as active site to promote the generation of reactive oxygen species (ROS). In addition, the slow-release effect of zinc ions (Zn2+) from ZnO contributed to the accelerated death of bacteria. As a result, under simulated sunlight conditions, the ZnO/NC-400(1 h) Schottky heterojunction demonstrated an impressive antibacterial efficiency of 99.33 % against Escherichia coli, consistently exceeding 95 % in repeated experiments. This work presents a controllable and encouraging approach for constructing heterojunction with effective antibacterial properties.

The Z-Scheme MIL-88B(Fe)/BiOBr Heterojunction Promotes Fe(III)/Fe(II) Cycling and Photocatalytic-Fenton-Like Synergistically Enhances the Degradation of Ciprofloxacin.

The Z-scheme MIL-88B/BiOBr (referred to as MxBy, whereas x and y are the mass of MIL-88B(Fe) and BiOBr) heterojunction photocatalysts are successfully prepared by a facile ball milling method. By adding low concentration H2 O2 under visible light irradiation, the Z-scheme heterojunction and photocatalytic-Fenton-like reaction synergistically enhance the degradation and mineralization of ciprofloxacin (CIP). Among them, M50B150 showed efficient photodegradation efficiency and excellent cycling stability, with 94.6% removal of CIP (10mgL-1 ) by M50B150 (0.2gL-1 ) under 90min of visible light. In the MxBy heterojunctions, the rapid transfer of photo-generated electrons not only directly decomposed H2 O2 to generate ·OH, but also improved the cycle of Fe3+ /Fe2+ pairs, which facilitated the reaction with H2 O2 to generate ·OH and ·O2 - radicals. In addition, the effects of photocatalyst dosages, pH of CIP solution, and coexisting substances on CIP removal are systematically investigated. It is found that the photocatalytic- Fenton-like reaction can be carried out at a pH close to neutral conditions. Finally, the charge transfer mechanism of the Z-scheme is verified by electron spin resonance (ESR) signals. The ecotoxicity of CIP degradation products is estimated by the T.E.S.T tool, indicating that the constructed photocatalysis-Fenton-like system is a green wastewater treatment technology.

Carbon quantum dots assisted BiFeO3@BiOBr S-scheme heterojunction enhanced peroxymonosulfate activation for the photocatalytic degradation of imidacloprid under visible light: Performance, mechanism and biotoxicity

A novel S-scheme heterojunction photocatalyst carbon quantum dots (CQDs)/BiFeO3/BiOBr (CBB) was synthesized via a facile hydrothermal method, which was highly effective in activating peroxymonosulfate (PMS) to photodegrade imidacloprid (IMD) (one of the typical neonicotinoid insecticides (NEOs)) under visible light irradiation. Based on the physicochemical and photoelectrochemical analysis, the super photocatalytic performance of the CBB photocatalyst was contributed to the enhanced separation and transfer of photogenerated electrons (e−) and holes (h+), the activation of PMS by reactive species, and the wider light absorption range induced by CQDs. Moreover, the intermediate products and possible photodegradation pathways of IMD were confirmed through high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS) detection and density functional theory (DFT) calculations. Although the photodegradation of IMD in the CBB/PMS/Vis system can be affected by the water quality parameters (i.e., acid group anions, pH, and the presence of humic acid (HA)), the synthesized CBB photocatalyst showed excellent photocatalytic performance in multiple natural water samples. This study provides a new idea to construct an effective and efficient heterojunction photocatalyst, which may have great advantages in photocatalytic degradation of NEOs and possibly other emerging contaminants in the aquatic environment.

Confined bismuth single atoms and nanoparticles dual-sites constructed via reverse etching for CO2 photoreduction to CH4

Synchronizing the directional photogenerated transfer of electrons and regulating the CO2 photocatalytic reduction process are key to achieving the efficient and highly selective photocatalytic reduction of CO2. The design of highly-dispersed active sites and the efficient collaboration of multiple sites are of great importance in attaining the above target. Herein, a reverse etching route was first proposed to confine Bi single atoms and nanoparticles as dual-sites for assisting CO2 photoreduction on TiO2, avoiding the mutual masking of the active sites. The Synergism of the dual-sites achieves the hydrodeoxygenation of * COOH and ushers the directional conversion of CO2 to CH4. Highly dispersed single Bi atoms could induce the transfer of photogenerated electrons, enhance CO2 absorption, and further provide active sites for reducing CO2 to *COOH intermediates. Besides, appropriate Bi nanoparticles could promote the separation and transfer of photogenerated and inhibit the formation of hydroxyl groups; more importantly, they could promote the release of protons, which would further accelerate the conversion of *COOH to CH4. After being integrated, the optimized dual-Bi/TiO2 catalyst achieves a CH4 generation rate of 103.89 μmol·g−1·h−1 with an impressive selectivity of 96.87 % as well as remarkable durability for photocatalytic CO2 reduction. This work provides new insights into developing robust catalysts through the artful design of synergistic catalytic sites for efficient photocatalytic CO2 conversion.

In situ irradiated XPS investigation on S-scheme TiO2/Bi2S3 photocatalyst with high interfacial charge separation for highly efficient photothermal catalytic CO2 reduction

The combination of S-scheme heterojunction and photothermal effect is a promising strategy to achieve efficient CO2 photoreduction into solar fuel due to the boosted charge carrier separation efficiency and faster surface reaction rate. Herein, unique photothermal-coupled TiO2/Bi2S3 S-scheme heterojunction nanofibers were fabricated and applied to a full-spectrum CO2 photoreduction system. Density functional theory calculation and experimental analyses have confirmed the generation of the internal electric field and the S-scheme electron transfer pathway, leading to a highly efficient charge carrier separation. Thanks to the excellent photothermal conversion capacity of Bi2S3, the photogenerated electron transfer rate, and surface reaction rate were further accelerated in hybrid photocatalysts. Under the synergistic effect of S-scheme heterojunction and photothermal effects, the optimal TiO2/Bi2S3 nanofibers achieved 7.65 μmol h–1 of CH4 production rate, which is 5.24 times higher than that of pristine TiO2. Moreover, the morphology reconstruction of Bi2S3 in hybrids facilitates the CH4 selectivity was significantly improved from 64.2% to 88.7%. Meanwhile, the CO2 photoreduction reaction route over TiO2/Bi2S3 nanofibers was investigated based on in-situ Fourier transform infrared spectra. This work provides some useful hints for designing highly efficient photothermal-coupled photocatalysts for CO2 photoreduction.

Single-atom Pt–N4 active sites anchored on porous C3N4 nanosheet for boosting the photocatalytic CO2 reduction with nearly 100% CO selectivity

Photoreduction of CO2 and H2O into fuels and value-added chemicals is a promising green technology for solar-to-chemical conversion. However, improving the conversion efficiency with regulated product selectivity is a big challenge due to the sluggish dynamic transfer and insufficient active sites. Herein, we report on Pt single atoms anchored porous C3N4 nanosheet photocatalyst (Pt1@CN) with Pt–N4 coordination for stable and efficient CO2 photoreduction using H2O as reductant. The Pt1@CN exhibits an evolution rate of 84.8 μmol g−1 h−1 with nearly 100% CO selectivity, outperforming most previous C3N4-based single-atom photocatalysts. Experimental and DFT calculation results reveal that the Pt–N4 coordinated active sites promote the photogenerated electron transfer, CO2 adsorption/activation, *COOH generation, and *CO desorption, thus accounting for the significantly improved CO2 photoreduction activity with ∼100% CO selectivity. This study provides a deep insight into the significant roles of single-atom active sites in enhancing the CO2 photoreduction activity and regulating the product selectivity.

Improved ultraviolet photodetector performances using solution-processed nitrogen-doped carbon quantum dots/ZnO hybrid thin films

We fabricated the solution-processed photodetectors using the nitrogen-doped carbon quantum dots/zinc oxide (NCQDs/ZnO) hybrid films and characterized using ultraviolet (UV) spot-light of 365 nm at 1 mW/cm2. The NCQDs adsorbed onto the surface and/or grain boundaries of ZnO crystallites control ZnO particle size (by capping) in the NCQDs/ZnO hybrid thin films, resulting in the improved film quality and decreased the dark current in the devices. The NCQDs to ZnO [%(w/v)] ratio of 1.2 × 10−3 in the hybrid film UV photodetector exhibits the stable and reproducible photoresponses with the highest responsivity & external quantum efficiency (which are ∼3 times higher), and detectivity (∼7.5 times higher) than the pristine ZnO based photodetector, attributed to the effective transfer of photogenerated electrons from NCQDs to ZnO nanoparticles in the hybrid film. The solution-processed NCQDs/ZnO hybrid films will be very much useful to improve the UV photodetector performances for the cost-effective commercial applications.

Photoelectrocatalytic CO2 conversion over carbon @ silicon carbide composites

Artificial photosynthesis, which utilizes sunlight to produce value-added chemicals and fuels from CO2, is a promising strategy to storage fluctuating solar energy and to realize zero carbon cycle simultaneously. While selective C2+ production via CO2 photoelectrocatalytic conversion remains a challenge due to the sluggish C-C coupling kinetics over current artificial photosynthesis catalysts. Herein, we present a carbon @ silicon carbide (C@SiC) catalyst for ambient CO2 photoelectric reduction under simulated solar irradiation, giving a CO2 conversion rate of 487 μmol∙gcat−1∙h−1 with an ethanol selectivity of 87.8%. The optimal sp2/sp3 carbon ratio of carbon layer not only facilitates the photo-generated electrons transfer from SiC to carbon layer, but also favors the C-C coupling kinetics of key intermediates for efficient CO2 to ethanol conversion.

Binary Ce-doped-ZnO/rGO composite as excellent photocatalyst for bromothymol blue dye degradation

Organic contaminants pose a grave danger to both the surroundings and public health, which emphasizes the urgent need for efficient decomposition techniques. Building a composite and adding a cocatalyst can both enhance the transfer of photogenerated electrons, which are useful strategies to increase photocatalytic efficiency. This study sought to synthesize cerium–doped ZnO–rGO nanoparticles with varying concentrations of Ce for visible–light photocatalytic degradation of bromothymol blue dye in water. The synthesized photocatalysts were characterized using transmission electron microscopy, x–ray diffraction, ultraviolet–visible spectrophotometry, energy dispersive spectroscopy, and scanning electron microscopy. The results disclosed that the photoactivity of the 0.6% Ce–ZnO–rGO was the highest and degraded 92% of bromothymol blue dye under visible light within 180 min (k = 1.072 ×10–2 min–1) compared to the pristine ZnO which only degraded the dye by about 22% (k = 1.15 ×10−3 min−1). The band gap of the pure ZnO was estimated to be 3.09 eV and that of the best performing composite (0.6% Ce) to be 2.81 eV which we suggest are responsible for the improved photodegradation. The pseudo–first–order photocatalytic kinetic has a strong correlation value of 0.99. The Ce–ZnO–rGO composites offer a lot of potential for cleaning the environment.

Defects materials of Institut Lavoisier-125(Ti) materials enhanced photocatalytic activity for toluene and chlorobenzene mixtures degradation: Mechanism study

In this paper, the effect of three monocarboxylic acids on MIL-125 synthesis was systematically investigated and the results were discussed in detail. X-ray diffractometry (XRD) and nitrogen adsorption–desorption curves indicated that small molecule acids (acetic acid, propionic acid and butyric acid) affected the morphology of MIL-125 and induced lamellar pores and structural defects in the crystals. Thermogravimetric measurements confirmed the presence of acid-regulated defective metal–organic frameworks (MOFs). Electrochemical tests and density function theory calculations indicated that acid modulation could change the forbidden bandwidth of the material. The acid modification strategy effectively promoted the transfer of photogenerated electrons and enhanced the adsorption and activation of O2 and H2O molecules, generating reactive radicals. The modified MOFs also showed excellent performance in the removal of mixed toluene and chlorobenzene. The degradation pathways of the mixture were analyzed by in situ infrared (IR) and gas chromatography-mass spectrometry (GC–MS). The mixture was converted to chlorophenolic intermediates in the presence of reactive oxygen species, further decomposed to form ethers and ethanol, and finally formed small molecules such as carbon dioxide and water. A feasible method was provided for the preparation of photocatalysts for the treatment of mixed VOCs.

Gradient graphitic carbon rings induce successive built-in electric field for photo-Fenton-like reaction

The heterojunction with matched energy band enables efficient peroxymonosulfate (PMS)-based photo-Fenton-like reaction. Nevertheless, the rapid photogenerated charge separation and transfer has been challenging. Herein, we precisely constructed an efficient heterogeneous photo-Fenton-like reactor with successive built-in electric field by gradient doping of coplanar graphitic carbon rings (Cgra) into cobalt tungstate/graphitic carbon nitride (CoWO4/GD-CN) heterostructure. The as-prepared CoWO4/GD-CN exhibited remarkable enhancement with a tetracycline hydrochloride degradation rate constant (0.776 min−1) higher than that of CoWO4/CN (0.507 min−1). Theoretical and experimental results demonstrated that the successive built-in electric field enhanced by gradient-doped coplanar Cgra ring accelerated photogenerated electrons transfer from the innermost to the outmost layer of CoWO4/GD-CN. This transfer drove Co(III)/Co(II) conversion for accelerated PMS activation, leading to enhanced degradation reactivity. CoWO4/GD-CN had excellent degradability towards representative contaminants, including carbamazepine (1.0 min−1), 4-chlorophenol (0.920 min−1), sulfamethoxazole (0.90 min−1), bisphenolA (0.933 min−1), atrazine (0.829 min−1), ciprofloxacin (0.589 min−1) and norfloxacin (0.617 min−1) in CoWO4/GD-CN/PMS/vis system, respectively. This work provided a novel insight into the gradient-dope modulated photo-Fenton-like reaction and guided the design of efficient photo-Fenton-like reactor.