Photodegradation Intermediates Research Articles

Construction of MOF@COF Z-scheme heterojunction for efficient photocatalytic degradation of tetracycline in water: synthesis, mechanism, degradation pathway, and DFT calculation

As emerging pollutants, antibiotics in water environment posed a significant threat to human health and ecosystem. A lot of attention has been focused on tetracycline (TC). Photocatalysis, a green and efficient water treatment technology, has shown broad application prospects. Currently, the construction of photocatalytic heterojunctions is often limited to matching suitable energy band structures. However, simple surface doping largely restricted the carriers transport efficiency and stability. In this study, a series of composite photocatalysts (designated as NMSN-x) were prepared by functionalized metal organic framework Ti-MOF and covalent organic framework SNW-1 for TC removal. The schiff-based reaction was employed to achieve covalent linkage between the monomer catalysts, which greatly enhanced the carrier transport efficiency of the composite photocatalysts. Under UV light, the NMSN-1.5 demonstrated impressive removal capability to TC, which removed 93.10 ± 2.86% of TC in 60minutes and achieved 61.37 ± 2.18% under visible light, with up to 76.51 ± 3.37% removal in a natural water background. Carrier separation and transfer was greatly enhanced by the covalent connection between the monomers forming the heterojunction. Combined with density functional theory, the electron transfer mechanism was identified as Z-scheme heterojunction. In addition, the photodegradation intermediates of NMSN-1.5 were assessed to be significantly less environmentally toxic than TC itself. This study introduced a novel strategy for constructing photocatalytic heterojunctions for removal of TC, serving as a valuable reference in the field.Keywords

Photochemical fate of nonionic polyacrylamide induced by hydroxyl radicals in the natural water: Mineralization mechanism exploration and half-life time evaluation

Water-soluble polyacrylamide (PAM) compounds have been used extensively in various sectors. The abundance of PAM in the environment raises concerns about its environmental impact. However, the mineralization of PAM in water under natural light irradiation remains insufficiently explored. This study utilizes nonionic PAM (nPAM) as a representative model to investigate both the mechanism and efficiency of nPAM degradation in water when exposed to ultraviolet (UV) light with hydrogen peroxide (H2O2) as the hydroxyl radical source. In the dark or with only UVA irradiation, negligible mineralization of nPAM occurred. In contrast, the presence of hydroxyl radicals (produced by the UVA/H2O2 system) produced 50 % nPAM mineralization over 7 days under our experimental conditions. The corresponding molecular weight (MW) of the nPAM was swiftly reduced from 1.58 ×106 Da to 1.59 ×103 Da in 3 days. Moreover, five carboxylic acids and nitrate ions were identified as the photodegradation intermediates of nPAM. The efficiencies of nPAM photodegradation by the UVA/H2O2 system in different natural waters and environmental conditions were assessed. The rate constant for the reaction between the hydroxyl radical and nPAM was 2.17 ×109 M-unit−1 s−1. The half-lives of nPAM in the sea and continental surface waters were determined to be several years and dozens of days, respectively. The application of UVB obviously accelerated the mineralization of nPAM in ultrapure water (71 % degradation in 7 days). Moreover, mineralization of concentrated nPAM (200 mg/L) in sea water was more efficient when both UVA- and UVB-activated H2O2 were used. Additionally, toxic acrylamide was not generated during nPAM photodegradation. Moreover, the photodegradation intermediates from nPAM were found to be neither acutely nor chronically toxic to aquatic organisms. This comprehensive study sheds light on the photochemical fate of nPAM in natural waters and provides essential insight for practical treatment of PAM in water systems.

Evaluation of tetracycline photocatalytic degradation using NiFe2O4/CeO2/GO nanocomposite for environmental remediation: In silico molecular docking, antibacterial performance, degradation pathways, and DFT calculations

Graphene-based nanostructures with distinct structural and physicochemical characteristics may be able to photodegrade antibiotics effectively. Herein, this study reports the successful synthesis of NiFe2O4/CeO2/GO nanocomposite (NC) by anchoring NiFe2O4/CeO2 to the surface of GO (Graphene oxide). All state-of-the-art characterization techniques investigated the nanostructure, crystallinity, phonon modes, chemical composition analysis, elemental composition, surface area, magnetic properties, and optical band gap. Hydrothermal approach assisted NiFe2O4/CeO2/GO catalyst showed better charge carrier separation and prompted the tetracycline (TC-HCl) photocatalytic degradation under visible light. Following 90 min of exposure to visible light, NiFe2O4/CeO2/GO nanocomposite demonstrated superior photocatalytic activity, with a TC-HCl degradation rate of 95%. Reasonable mechanisms of tetracycline degradation were proposed where the •OH and •O2- played a leading role based on identified intermediates. Moreover, tetracycline photodegradation intermediates and the optimal pathway were identified using LC-MS spectrometry. This study alsoperformed Density Functional Theory (DFT) calculations for the preparedmaterials to validate the experimental data. In vitro, antibacterial studies were consistent with the molecular docking investigations of the NiFe2O4/CeO2/GO nanocomposite against DNA gyrase and FabI from Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Lastly, the outcomes revealed a new potential for NiFe2O4/CeO2/GO nanocomposite for improved photocatalytic performance, making it a promising photocatalyst for wastewater treatment.

Direct Z-scheme charge transfer Bi2O3/UiO-66-NH2 heterojunctions for boosted photocatalytic degradation of tetracycline hydrochloride in different water systems

The development of hybrid heterostructure photocatalysts with enhanced visible light absorption capacity holds significant importance in environmental remediation. However, the challenge persists in exploiting strong visible-light responsive photocatalysts with both high efficiency and stability. Herein, we successfully synthesized a hybrid Z-scheme heterojunction of Bi2O3 and UiO-66-NH2 (Bi2O3/UiO-66-NH2) through a simple hydrothermal route. The visible light photocatalytic performance of Z-scheme Bi2O3/UiO-66-NH2 heterojunction is systematically evaluated for persistent antibiotic tetracycline hydrochloride (TC-HCl) both in the clean and real water matrix. All heterojunction catalysts exhibit superior photodegradation capabilities compared to pristine Bi2O3 and UiO-66-NH2. The optimal ratio of the two components heterojunction (BUN-150), in particular, demonstrates the highest removal efficiencies for TC-HCl (95 %) within a 90-min timeframe. This remarkable photocatalytic performance is credited to the Z-scheme charge transfer occurring at the interface of Bi2O3 and UiO-66-NH2 in Bi2O3/UiO-66-NH2 heterojunction. The active species experiments and electron paramagnetic resonance analyses are conducted to identify the active reactive species during the TC-HCl degradation (·OH, h+, and ·O2−), and a precise photocatalytic degradation mechanism is explained. Additionally, the photodegradation intermediates of TC-HCl are detected using the HPLC-MS analysis to explain the degradation pathways of TC-HCl. This research paves the way for the development of novel Z-scheme Bi2O3-based heterojunction catalysts for outstanding photocatalytic applications.

Integrated approach for sustainable degradation of tolperisone hydrochloride from water by photodegradation: Chemometrics, chemical kinetics, intermediates, and environmental toxicity assessment

Even though we have only one planet to live on, environmental pollution is still an urgent global issue. Among all-natural threatened resources, the drinkable water has one of the most burdening influences on the life quality and economy. The pharmaceutically active ingredients are the most concerning pollutants. In this study, heterogeneous photocatalysis was used as a sustainable alternative for tolperisone hydrochloride (TLP) removal from water. The degradation pathway of TLP was also analyzed using various scavengers and it was found that the contribution of reactive species changed in following order: OHfree· ˃ h+ ≫ OHads· > e-. Furthermore, 12 photodegradation intermediates of TLP were identified using LC–ESI–MS/MS. In addition, the toxicity of TLP and its degradation intermediates were examined on barley, using chemometrics. The most significant variations were observed on barley plant after 4 days of germination and on the root, during the barley biomass production. The results also showed that TLP and its intermediates are harmful to the plants, due to deteriorating water uptake with toxic TLP-compounds that reach the vital parts of plants. Also, slightly variations in total nitrogen amount were observed. The high genetic variability efficiently guards barley from various environmental stresses.

Construction of Z-scheme NiO/BiOBr heterojunction for facilitating photocatalytic degradation of oxytetracycline and 2-mercaptobenzothiazole

Z-scheme NiO/BiOBr heterojunction was prepared by mechanical ball milling method and applied for the photodegradation removal of oxytetracycline (OTC) and 2-mercaptobenzothiazole (MBT). The Z-scheme electron transport pathway optimizes the separation of photogenerated carriers, thereby significantly increasing the generation capacity of reactive oxygen species (ROS). The photocatalytic degradation experiments demonstrate that the optimized OTC and MBT removal efficiency of NiO/BiOBr (NBOB) composites could reach 72.6% (120 min) and 97.7% (9 min), respectively. Photoluminescence (PL) spectra and PL decay curves indicate that NBOB-2 composites exhibit low photoinduced electron-hole recombination rate and accelerated electron separation efficiency. In addition, ESR spectra confirm that the Z-scheme NiO/BiOBr heterojunction can generate a larger quantity of ROS species. The possible photodegradation pathways and toxicity analysis for the OTC and MTB photodegradation intermediates are elucidated by HPLC-MS measurement and T.E.S.T. application. The manuscript provides a reference for the macro-preparation of bismuth-based photocatalysts with superior performance and high stability.

Cornstalk hydrochar produced by phosphoric acid-assisted hydrothermal carbonization for effective adsorption and photodegradation of norfloxacin

Hydrochars have been widely applied in removing pollutants from aqueous solutions. In this study, hydrochars synthesized by H3PO4-assisted hydrothermal carbonization (HC-xPs) were used to remove norfloxacin (NOR) from water through synergistic adsorption and photodegradation. HC-xPs showed the morphology of carbon microspheres with an average diameter of 0.3 μm. The specific surface area of the hydrochar carbonized with 5 mol/L H3PO4 (HC-5P) was 11.2 times higher than that of the pristine hydrochar (HC). Furthermore, phosphorus-containing functional groups were introduced to HC-5P, beneficial to its adsorption of NOR. The highest NOR adsorption was achieved on HC-5P with the maximum Langmuir capacity of 69.1 mg g−1, owing to multiple mechanisms including electrostatic effects, π-π interactions, hydrophobic interactions, and hydrogen bonding. Compared with HC, HC-5P also demonstrated increased visible light absorption capacity. The first-order rate constant of HC-5P on combined adsorption and photodegradation of NOR was 12.0 times of HC. The photodegradation intermediates were identified by HPLC-MS to understand NOR degradation pathways. This work can be extended to the preparation of low-cost and highly efficient hydrochars for adsorption and photodegradation of pollutants in water.

Boosted Photocatalytic Performance for Antibiotics Removal with Ag/PW12/TiO2 Composite: Degradation Pathways and Toxicity Assessment.

Photocatalyst is the core of photocatalysis and directly determines photocatalytic performance. However, low quantum efficiency and low utilization of solar energy are important technical problems in the application of photocatalysis. In this work, a series of polyoxometalates (POMs) [H3PW12O40] (PW12)-doped titanium dioxide (TiO2) nanofibers modified with various amount of silver (Ag) nanoparticles (NPs) were prepared by utilizing electrospinning/photoreduction strategy, and were labelled as x wt% Ag/PW12/TiO2 (abbr. x% Ag/PT, x = 5, 10, and 15, respectively). The as-prepared materials were characterized with a series of techniques and exhibited remarkable catalytic activities for visible-light degradation tetracycline (TC), enrofloxacin (ENR), and methyl orange (MO). Particularly, the 10% Ag/PT catalyst with a specific surface area of 155.09 m2/g and an average aperture of 4.61 nm possessed the optimal photodegradation performance, with efficiencies reaching 78.19% for TC, 93.65% for ENR, and 99.29% for MO, which were significantly higher than those of PW12-free Ag/TiO2 and PT nanofibers. Additionally, various parameters (the pH of the solution, catalyst usage, and TC concentration) influencing the degradation process were investigated in detail. The optimal conditions are as follows: catalyst usage: 20 mg; TC: 20 mL of 20 ppm; pH = 7. Furthermore, the photodegradation intermediates and pathways were demonstrated by HPLC-MS measurement. We also investigated the toxicity of products generated during TC removal by employing quantitative structure-activity relationship (QSAR) prediction through a toxicity estimation software tool (T.E.S.T. Version 5.1.2.). The mechanism study showed that the doping of PW12 and the modification of Ag NPs on TiO2 broadened the visible-light absorption, accelerating the effective separation of photogenerated carriers, therefore resulting in an enhanced photocatalytic performance. The research provided some new thoughts for exploiting efficient and durable photocatalysts for environmental remediation.

Band structure induced photodegradation mechanism of PEI-based carbon quantum dots for tetracycline and toxicity evaluation for these intermediates

Many kinds of carbon quantum dots (CQDs) are already released into the environment, and the factor that determine the photodegradation ability of these CQDs for antibiotics is still unclear. Herein, three PEI-based CQDs (CAPEI, HAPEI and BCNPEI) were prepared by hydrothermal method to clarify the structural factors that determine their photodegradation performance against tetracycline (TC) when exposed to visible light. Experimentally, BCNPEI photodegraded 62 % of TC, while CAPEI and HAPEI photodegraded TC only about 5–8 %. Sizes, functional groups, aromaticity and energy band structures of these CQDs have been analyzed, and the energy band structure has the best linear relationship with the photodegradation properties of CQDs on TC. The conduction band (CB) value of BCNPEI is − 0.623 V and the valence band (VB) value is 2.207 V, which are strong enough to produce hydroxyl radicals (·OH) and superoxide radicals (·O2-) under visible light exposure. And this has been verified with photoactive species capture experiments and ESR experiments. Thus, band structure is the factor that determine the photocatalytic performance of CQDs for TC. Furthermore, a possible photodegradation pathway of TC by CQD was proposed in a study of high-performance liquid chromatography-mass spectrometry (HPLC-MS) results. The photodegradation intermediates of TC were less toxic than TC, suggesting that the photodegradation of TC by CQD can reduce its environmental risk. In this study, valuable insights are provided into the behavior of CQDs exposed to the environment.

Triple-mechanism driven Fe-doped n-n hetero-architecture of Pr6O11-MoO3 decorated g-C3N4 for doxycycline degradation and bacterial photoinactivation

Photocatalysis is a clean technology that can be applied to water treatment processes. In this study, we have constructed n-n heterojunction between Fe-doped Pr6O11-MoO3 and g-C3N4 with a flower-on-sheet morphology (Fe/Pr6O11-MoO3@g-C3N4 NCs). The fabricated nanomaterials were characterized using XRD, XPS, SEM, TEM, SAED, EDX, elemental mapping, PL, DRS, BET, EIS and ESR. The photogenerated charge carriers were produced through three routes - internal electric field caused by n-n heterojunction, dynamic cycling of Fe3+/Fe4+ and Pr3+/Pr4+ metal-oxidation states due to photo-Fenton processes, and the interstitial defect states caused by Fe doping. Interestingly, 30-FPMG NCs attained 98% doxycycline degradation in 280 min and 95% S. epidermis bacterial photoinactivation at 50 mg/L dosage. Here, OH was the primary ROS involved in the photocatalytic process. The effects of NPs dosage, drug concentration, pH and ions were tested. The stability was examined for six consecutive cycles. The photodegradation intermediates were predicted using GC–MS and ECOSAR software was used to assess their toxicity.

Significantly activated persulfate by novel carbon quantum dots-modified N-BiOCl for complete degradation of bisphenol-A under visible light irradiation

The practical application of bismuth-based photocatalysts in the field of micropollutant photodegradation is limited due to their weak light absorption and rapid charge recombination. Herein, we have developed a novel carbon quantum dots-modified N-BiOCl (CDs-N-BiOCl) photocatalyst to activate persulfate (PS) for the complete elimination of endocrine-disruptor bisphenol A (BPA) under visible light irradiation. The photoelectric properties characterization shows that N atoms could replace Cl atoms or adsorb on Bi atoms to form local N 1s states in the BiOCl lattice, accompanied by the introduction of doping energy levels that shorten the electron migration distance. Meanwhile, the decorated CDs could effectively accept the photoinduced electrons from N-BiOCl conduction band to facilitate the charge separation. Thus, the 7%CDs-N-BiOCl (7CNB) nanocomposite synergistically activated PS realized rapid and effective degradation of BPA within 20 min (degradation efficiency and mineralization reached 100 % and 66.4 % respectively). Moreover, the 7CNB/PS system displayed favorable adaptability, durability, and interference resistance. Furthermore, the biotoxicity experiments demonstrated that the photodegradation intermediates promoted the growth of Escherichia coli which indicates its eco-friendliness for practical application. Finally, the electron transfer mechanism and the formation of reactive oxygen species in the photodegradation process were interpreted. In short, this work will present a promising strategy for bismuth-based photocatalysts to be used for the efficient treatment of real water bodies under visible light irradiation.

Photocatalysis Combined with Microalgae to Promote the Degradation and Detoxification of Tetracycline Hydrochloride

The continuous discharge of antibiotics into the environment poses a serious threat to the ecological environment and human health. In this study, photocatalysis and microalgae were combined to study the removal of tetracycline hydrochloride (TCH) and its photodegradation intermediates in water. The results showed that after photocatalytic treatment, the removal rate of TCH reached 80%, but the mineralization rate was only 17.7%. While Chlorella sp. alone had poor tolerance to high concentrations of TCH, the combined treatment of photocatalysis and microalgae completely removed TCH and increased the mineralization efficiency to 35.0%. Increased cell density was observed, indicating that TCH and the intermediates produced in the photocatalysis process could be utilized by algae for growth. Meanwhile, TCH degradation pathways were proposed based on Liquid Chromatograph Mass Spectrometer analysis, and the toxicity of intermediates detected was predicted using ECOSAR software, which showed that the type and quantity of highly toxic intermediates decreased significantly after subsequent algal treatment. The results demonstrate that photocatalysis and microalgae combined treatment is an efficient and eco-friendly method for the removal of antibiotics in water.

Fast monitoring of organic dye degradation coupled with a colorimetric approach in a Ag-modified TiO2 nanotube photocatalytic system

Monitoring the contents of organic dyes in real-time is crucial for the valuation of photocatalyst performance. To achieve this, a method of detecting organic dyes was designed based on color variations by using Ag nanoparticle modified TiO2 nanotubes (Ag/TiO2) as photocatalysts. The obtained Ag/TiO2 photocatalyst possesses strong visible-light absorption, and 1.0% Ag/TiO2 exhibited the best performance under UV and simulated sunlight. The investigation indicates that the photocatalytic activity of TiO2 nanotubes is greatly improved by the modification with silver. Moreover, the photodegradation intermediates and pathways are demonstrated by trapping experiments and density functional theory calculations. To quantitatively determine the concentration of methyl orange, a partial least squares model was built using RGB values and the concentration of a methyl orange solution. This finding provides a new idea to fabricate a sensor for point-of-care test of organic dyes in the field of environmental applications.

Photodegradation of a mixture of five pharmaceuticals commonly found in wastewater: Experimental and computational analysis

Photochemical transformation of pharmaceuticals plays an important role in their natural attenuation, especially in lagoon-based wastewater treatment plants and surface waters receiving substantial sunlight. In this study, the photodegradation of five important pharmaceuticals was studied in samples obtained from a wastewater treatment plant and surface water sources. Batch photodegradation studies for a mixture of pharmaceuticals (diclofenac, sulfamethoxazole, acetaminophen, carbamazepine and gemfibrozil) were carried out in a photochemical reactor. Multiple aliquots of samples removed from the reactor during the experiment were analyzed through high-performance liquid chromatography (HPLC) coupled to a photodiode array (PDA) detector. Intermediate products formed due to photodegradation were identified by ultra-high-performance liquid chromatography coupled with a time-of-flight mass spectrometry (UHPLC-MS/MS). Diclofenac and sulfamethoxazole were found to undergo direct photodegradation due to strong light absorption, whereas the indirect route of photosensitized degradation in the presence of dissolved organic matter (DOM) and model humic acid was significant for acetaminophen, carbamazepine, and gemfibrozil. The reactive radicals such as hydroxyl (OH•), singlet oxygen (1O2) and excited states of DOM (*DOM) were predominantly responsible for the indirect photodegradation of acetaminophen, gemfibrozil and carbamazepine, respectively. Computational analysis revealed that chlorine and carbon atoms belonging to the benzene ring of diclofenac were more reactive to radical attack. Sulfamethoxazole photodegradation occurred through oxidation of the NH2 group. Acetaminophen was more susceptible to electrophilic radical attack at the O-11, and N-7 positions and carbon atoms ortho to the phenolic oxygen and the amine group. The double bonds between C-7, C-8 and C-13 were the most reactive sites for carbamazepine that participated in the phototransformation pathway. Organic matter plays a critical role in the photodegradation of emerging contaminants. The coupling of DFT calculations with UHPLC-MS/MS analysis provided insights on key functional groups participating in the phototransformation pathway. Thus, both parent pharmaceuticals and the photodegradation intermediates should be considered during wastewater treatment.

Efficient photodegradation of disulfine blue dye and Tetracycline over Robust and Green g-CN/Ag3VO4/PAN nanofibers: Experimental design, RSM, RBF-NN and ANFIS modeling

The g-CN/Ag3VO4/PAN nanofibers (NFs) is prominent from various nanophotocatalysts (NPCs) due to their higher surface to volume ratio, mechanical strength and recyclable characteristics. In this study, g-CN/Ag3VO4/PAN NFs were obtained through in situ method by immobilizing Ag3VO4 on g-CN/PAN NFs. Compared to g-CN/PAN and Ag3VO4/PAN, the g-CN/Ag3VO4/PAN NFs revealed excellent photocatalytic performance toward disulfine blue dye (DB). Also, the g-CN/Ag3VO4/PAN NFs showed highly activity over some interference of inorganic cations/anions and excellent cycling stability. Furthermore, the batch experiments designed by central composite design (CCD) were employed for remove of tetracycline (TC). Afterward, response surface methodology (RSM), Radial basis function artificial neural network (RBF ANN) and an adaptive neuro-fuzzy inference system (ANFIS) have been used for modeling of photocatalyst dose, concentration of TC and irradiation time. Due to strong influence of pH on the photocatalytic degradation, the pH was optimized as one at a time variable. For all three models, the values of the statistical parameters were calculated. The obtained results reveal that the ANFIS models is more accurate to predict the degradation of TC. Furthermore, the effective factors were optimized by employing the Desirability function (DF) and genetic algorithm (GA) approach and then used for real water samples. At this optimum condition, the removal percentage was obtained ∼97% by DF and GA approach, respectively. At the end, the LC-Mass method was employed to detect the intermediates of photodegradation of TC molecules.

Photocatalytic degradation of oxytetracycline with the REMs (Er, Tm, Yb)-doped nickel and copper aluminates

Oxytetracycline (OTC) is an antibiotic drug. It is widely used in veterinary, animal husbandry, and agriculture. Antibiotics are emerging environmental pollutants. We propose an efficient photocatalytic method for remediation of aqueous reservoirs from OTC. We synthesized erbium-, thulium- and ytterbium-doped nickel and copper aluminates. The doped samples have better dispersion, higher specific surface areas (188 m2 g−1 for Er-NA) and decreased energy band gaps. The doping of nickel and copper aluminates (NA and CA) significantly improved the photocatalytic performance. Er-CA was the most photoactive. The Er-doping of NA and CA increased photodegradation efficiency from 27 to 73 % and from 65 to 90 %, respectively. The LC-MS analysis allowed to identify the major intermediates of OTC photodegradation. The photocatalytic metabolites were hemocompatible and did not present cytotoxicity towards monocytic cells. We envisage a great potential of the rare-earth-metal-doped semiconductors in the removal of emerging environmental pollutants.

Bismuth molybdate photocatalyst for the efficient photocatalytic degradation of tetracycline in water under visible-light irradiation

Based on a solvothermal method using Bi2MoO6 (BMO) as the raw material, a novel BiOCl BMO photocatalyst with a flower-like spherical structure was synthesized. The photocatalytic activity of this catalyst was evaluated using a Xe lamp (λ ≥ 420 nm) to simulate sunlight. The crystal structure, morphology, and photochemical characteristics of the BiOCl–BMO photocatalyst were characterized by X-ray diffractometry, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, UV-vis spectroscopy, Raman spectroscopy, photoluminescence measurements, and electrochemical impedance spectroscopy. Under visible-light irradiation, 50 mg BiOCl–BMO with a BiOCl/BMO mass rate of 0.06 degraded 97.23% of a tetracycline (TC) hydrochloride solution (50 mL, 10 mg/L) within 100 min, with a mineralization rate of 81.22%. Free-radical capture experiment revealed that the •OH, •O2−, h+, and e− species (and in particular •OH and •O2−) promoted TC degradation. Furthermore, the active free radicals and TC photodegradation intermediates were identified, and the mechanism and degradation pathways of TC photodegradation by the heterojunction structures were proposed. This study describes an efficient catalyst for the removal of TC from water and introduces a new approach that could be applied in the design of other Bi-based photocatalysts with excellent photocatalytic properties. At the same time, the developed system is of great significance for the efficient removal of TC from aqueous environments.

Ternary TiO2@Bi2O3@TiO2 hollow photocatalyst drives robust visible-light photocatalytic performance and excellent recyclability

The development of visible-light photocatalysts with excellent catalytic activity and recyclability still remains a big challenge. Here, we present a facile template and self-assemble strategy to design new confined ternary photocatalyst by embedding Bi2O3 (p-type) into hierarchical hollow TiO2 (n-type) spheres (TiO2@Bi2O3@TiO2). The obtained TiO2@Bi2O3@TiO2 photocatalyst exhibits strong visible-light absorption and efficient charge separation due to its unique n-p-n heterojunction, effectively driving the complete degradation (100%) of tetracycline according to the characteristic peak (∼350 nm) and TOC results of TC under visible light (λ > 420 nm). Interestingly, the introduction of confinement effect considerably promotes cyclic stability, especially in a strong acid (pH=3.0) or alkali (pH=11) environment. Moreover, the photodegradation intermediates and pathways are demonstrated by LC-MS measurement. This finding provides a new idea to design other confined photocatalysts with a ternary heterojunction for clean energy and environment applications.

N-CQDs from reed straw enriching charge over BiO2−x/BiOCl p-n heterojunction for improved visible-light-driven photodegradation of organic pollutants

Green bismuth-based photocatalysts have attracted extensive attention in the field of PPCPs photodegradation. The improved carrier separation efficiency still remains a key factor to enhance photocatalytic performance. Herein, N-doped biomass carbon quantum dots (N-CQDs) decorated p-n heterojunction photocatalyst BiO2−x/BiOCl was prepared using a facile ion-etching strategy, and it displayed a markedly enhanced catalytic activity in the photodegradation of sulfonamide antibiotics. Calculated by the differential charge density, the doped N-CQDs could gather photogenerated electrons, which indicated that the introduction of N-CQDs into BiO2−x/BiOCl would effectively inhibit the recombination of photogenerated charge carriers. In addition, photocatalytic performance and density functional theory (DFT) calculation results revealed that the photogenerated electrons tended to transfer from p-BiOCl to n-BiO2−x through N-CQDs, which could generate ·O2- and photogenerated h+ to oxidize the target pollutants. Benefiting from the synergistic effect of accelerated separation of e--h+ in p-n heterojunction and the electron-rich performance of N-CQDs, the superb TOC removal efficiencies (89.40% within 120 min visible-light irradiation) and toxicity reduction performance of photodegradation intermediates were achieved. As a consequence, this work will provide a design of high-quality photocatalysts and a green-promising strategy for bismuth-based photocatalysts in the water treatment of PPCPs.

Coupling band structure and oxidation-reduction potential to expound photodegradation performance difference of biochar-derived dissolved black carbon for organic pollutants under light irradiation

Herein, the photodegradation performances difference of rice straw biochar-derived dissolved black carbon (DBC) for Tetracycline and Methylene Blue under visible light irradiation have been investigated. Tetracycline is easier degraded (degradation rate: 68%), followed by Methylene Blue (degradation rate: 14%). Singlet oxygen (1O2), superoxide radicals (O2−), holes (h+) and triplet DBC (3DBC*) are all make contribution for Tetracycline degradation by DBC, whereas just singlet oxygen (1O2), superoxide radicals (O2−) and 3DBC* are involved in the MB degradation by DBC. Singlet oxygen (1O2) maybe from the fulvic acid-like structure of DBC, while band structure of DBC can explain why superoxide radicals (O2−) and holes (h+) can be formed, whereas hydroxyl radicals (OH) cannot be formed. The oxidation-reduction potential results of Tetracycline and Methylene Blue suggests that Tetracycline is easier to be oxidized than Methylene Blue as well as Methylene Blue is easier to be reduced than Tetracycline. Furthermore, experimental and theoretical results support that DBC has good interaction with Tetracycline, but the interaction between DBC and Methylene Blue is very weak. This likely explain why holes (h+) is not detected for Methylene Blue degradation by DBC since Methylene Blue has not too much chance to meet holes (h+). TC photodegradation intermediates are less toxic than Tetracycline based on QSAR method. Two possible photodegradation path of Tetracycline by DBC are proposed according to HPLC-MS results.