Internal electric fields drive dual S-scheme heterojunctions: Insights into the role of the triple interlaced lattice

Tourmaline/pyrite dual mineral photocatalysis with a powerful surface electric field for efficient antibiotic removal

Pyrite (FeS2) has garnered attention due to its narrow bandgap, high light absorption, and low cost. However, the rapid recombination of charge carriers hinders its practical application. Surface electric field is a unique characteristic of tourmaline, which can induce effective separation of photo generated electrons and holes. This study successfully combined two directly mined natural minerals, tourmaline and pyrite, to form TFS. Characterization and experiments show that the surface electric field of tourmaline can significantly enhance the photocatalytic activity of TFS. Tetracycline (TC, 50 ppm) was degraded by 95% with 60 min, and the TFS reaction rate constant reached 0.0439 min-1, which is 6.1 times and 17.3 times higher than that of tourmaline and FeS2. Additionally, it significantly improved light absorption and charge carrier separation capabilities. After simulating various natural environmental factors, TFS demonstrated practicality. Considered analysis of active substances and detection revealed that h+ and 1O2 radicals are significant contributors, and the photocatalytic mechanism was proposed. Furthermore, the transformation pathways and toxicity of metabolites were studied. This research offers further inspiration and insights for improving photocatalytic material performance and the green governance environment of natural resources.

Electric field driven tourmaline/hematite dual mineral photocatalysis for efficient antibiotic removal

Hematite (Fe2O3) has garnered attention due to its stability, economic viability, and non-toxic nature. However, the rapid recombination of charge carriers hampers its practical application. On the other hand, tourmaline's inherent surface electric field facilitates the rapid separation of photogenerated electrons and holes. In this study, two directly mined natural minerals, tourmaline and hematite (TFO), were successfully combined. Characterization and experiments indicate that the pronounced enhancement of photocatalytic activity in Fe2O3 is attributed to the electric field effect on the surface of tourmaline. TFO successfully removes 93% of tetracycline (TC, 50 ppm) within 60 min. The reaction rate constant for TFO composite material (0.0410 min-1) is 8.5 times that of tourmaline (0.0048 min-1) and 14.1 times that of hematite (0.0029 min-1). Simultaneously, it markedly improves light absorption and charge carrier separation capabilities. Through simulations of various natural environmental factors, TFO demonstrates excellent practicality. Analyzing and detecting active species revealed the involvement of four types of active species, with ·OH radicals making the most significant contribution. The photocatalytic mechanism was proposed. Furthermore, the degradation pathway of tetracycline and the toxicity of its metabolites were investigated. This work provides additional inspirations and insights for photocatalytic materials performance enhancement and natural resources green governance environment.

Integrating the 2D/2D heterostructure of the MXene monolayer and BiOBr nano-sheets for superior photo-catalysis

The highly efficient photo-oxidation of alcohols has sparked significant potential to cope with environmental pollution and the ever-increasing energy crisis. This study reports a unique Ti3C2/BiOBr (TB) heterojunction with a rich inter-face based on in situ exfoliation of MXene and subsequently anchored onto BiOBr sheets. The TB nano-composites exhibited substantially improved photo-catalytic activity towards the photo-oxidation of benzyl alcohol (BA) to benzaldehyde and achieved a formation rate of 1.73 mmol g-1 h-1, greater than pristine BiOBr. The ultra-thin inter-facial contact boosted the oxygen vacancies (Ov) and Ti3+ and possessed the most negative adsorption energy, which boosted the transfer and separation of inter-facial charge carriers and the adsorption and dissociation of BA. Overall, the successful synthesis of TB composite, along with its exceptional photo-catalytic performance, offers valuable insights for applications in green chemistry and environmental remediation.

Exquisitely designed TiO2 quantum dot/Bi2O2CO3 nano-sheet S-scheme heterojunction towards boosted photo-catalytic removal

The development of novel semiconductor photo-catalysts for the efficient degradation of antibiotics poses a considerable challenge in the context of ever-increasing environmental pollution. Herein, an S-scheme photo-catalyst consisting of TiO2 quantum dots (QDs, size ∼4-6 nm) anchored on Bi2O2CO3 nano-sheets was synthesised via a facile hydrothermal protocol. TiO2/Bi2O2CO3 (TB) nano-composite exhibits enhanced photo-catalytic removal of tetracycline, achieving ∼0.0158 min-1 photo-degradation rates using visible light, which is 3- and 53-fold greater than that of pristine TiO2 and Bi2O2CO3, respectively. The theoretical calculations substantiate that the built-in electric field in the TB nano-composite is conducive to the separation and transfer of photo-excited carriers. Notably, the generated superoxide radicals rather than hydroxyl were identified as the responsible species for tetracycline degradation. In addition, the corresponding degradation pathway and eco-toxicity analysis were also elucidated. In conclusion, this work contributes valuable insights and presents a feasible approach for the fabrication of S-scheme photo-catalysts (TiO2 QDs and bismuth-based nano-materials), thereby enabling the efficient removal of water pollutants.

Methyl contributes to the directed phosphorus doping of g-C3N4: pH-dependent selective reactive oxygen species enable customized degradation of organic pollutants

In the photocatalytic degradation process, constructing a controllable composite oxidation system with radicals and nonradicals to meet the requirement for efficient and selective degradation of diverse pollutants is significant. Herein, a methylated and phosphorus-doped g-C3N4 (NPEA) can exhibit selective radical and nonradical species formation depending on the pH values. The NPEA can spontaneously switch the production of active species according to the pH value of the reaction system, exhibiting steady-state concentrations of ·O2- for 11.83 × 10-2 µmol L-1 s-1 (with 92.7 % selectivity) under alkaline conditions (pH = 11), and steady-state concentrations of 1O2 for 5.18 × 10-2 µmol L-1 s-1 (with 88.7 % selectivity) under acidic conditions (pH = 3). The NPEA exhibits stability and universality in the degradation of pollutants with rate constant for sulfamethazine (k = 0.261 min-1) and atrazine (k = 0.222 min-1). Moreover, the LC-MS and Fukui function demonstrated that the NPEA can tailor degradation pathways for pollutants, achieving selective degradation. This study offers a comprehensive insight into the mechanism of the photocatalytic oxidation system, elucidating the intricate interplay between pollutants and reactive oxygen species.

Interface engineering in a nitrogen-rich COF/BiOBr S-scheme heterojunction triggering efficient photocatalytic degradation of tetracycline antibiotics

Tetracycline (TC) antibiotics, extensively utilized in livestock farming and aquaculture, pose significant environmental challenges. Photocatalysis, leveraging renewable sunlight and reusable photocatalysts, offers a promising avenue for mitigating TC pollution. However, identifying robust photocatalysts remains a formidable challenge. This study introduces a novel hollow-flower-ball-like nanoheterojunction composed of a nitrogen-rich covalent organic framework (N-COF) coupled with BiOBr (BOB), a semiconductor with a higher Fermi level. The synthesized N-COF/BOB S-scheme nanoheterojunction features an expanded contact interface, strengthened chemical bonding, and unique band topologies. The N-COF/BOB composites showcased exceptional TC degradation performance, achieving an 81.2% removal of 60 mg/L TC within 2 h, markedly surpassing the individual efficiencies of N-COF and BOB by factors of 3.80 and 5.96, respectively. Furthermore, the total organic carbon (TOC) removal efficiency highlights a superior mineralization capacity in the N-COF/BOB composite compared to the individual components, N-COF and BOB. The toxicity assessment revealed that the degradation intermediates possess diminished environmental toxicity. This enhanced performance is ascribed to the robust S-scheme nanoheterojunction structure, which promotes efficient photoinduced electron transfer from BOB to N-COF. This process also augments the separation of photogenerated charge carriers, resulting in an increased yield of superoxide radicals (∙O2-) and hydroxyl radicals (∙OH). These reactive species significantly contribute to the degradation and mineralization of TC. Consequently, this study introduces a sustainable approach for addressing emerging antibiotic contaminants, employing COF-based photocatalysts.

Chitosan synergizes with bismuth-based metal-organic frameworks to construct double S-type heterojunctions for enhancing photocatalytic antimicrobial activity

In recent years, photocatalytic technology has been introduced to develop a new kind antimicrobial agents fighting antibiotic abusing and related drug resistance. The efforts have focused on non-precious metal photocatalysts along with green additives. In the present work, a novel bis-S heterojunctions based on the coupling of polysaccharide (CS) and bismuth-based MOF (CAU-17) s synthesized through a two-step method involving amidation reaction under mild conditions. The as prepared photocatalyst literally extended the light response to the near-infrared region. Owing to its double S-type heterostructure, the lifetime of the photocarriers is significantly prolonged and the redox capacity are enhanced. As a result, the as prepared photocatalyst indicated inhibition up to 99.9 % under 20 min of light exposure against Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria as well as drug-resistant bacteria (MRSA). The outstanding photocatalytic performance is attributed to the effective charge separation and migration due to the unique double S heterostructure. Such a double S heterostructure was confirmed through transient photocurrent response, electrochemical impedance spectroscopy tests and electron spin resonance measurements. The present work provides a basis for the simple synthesis of high-performance heterojunction photocatalytic inhibitors, which extends the application of CAU-17 in environmental disinfection and wastewater purification.

Revealing the synergistic effect between radical and non-radical species of sulfur-doped carbon nitride for ciprofloxacin removal: Based on density functional theory study

The distinct characteristics of active species produced during the photocatalytic reaction can result in alterations in the degradation routes of organic pollutants with diverse chemical structures. The relationship between the active species and degradation pathways of organic pollutants lacks a direct experimental or characterization method, so in-depth research is still needed to understand the details of their interactions. In this study, sulfur-doped bulk carbon nitride (SBCN) was prepared based on bulk carbon nitride (BCN), and the process of S-doping enhancing the production of O21 was revealed. Through the degradation experiment, the degradation rate of CIP by SBCN reached 91 %, which was higher than that of BCN (66 %). The increase of degradation rate was mainly attributed to the increase of O21. Through the density functional theory (DFT) calculation of CIP and its degradation intermediate, due to the preferential oxidation of CIP by O21, O21 changes the initial degradation direction of CIP, releasing more attack sites for ˙O2-, thereby achieving more efficient degradation of CIP through the synergy of O21 and ˙O2-. In this study, the attack preferences of the active species and their synergistic promotion provide important insights for the efficient photocatalytic degradation of organic pollutants.

Constructing 3D flower-like S-scheme N-Bi2O2CO3/g-C3N4 heterojunction with enhanced photocatalytic performance

Mineral processing wastewater contains a lot of organic matter and heavy metal ions, and poor self-degradation ability makes it a key treatment object in environmental treatment. Photocatalysis is a promising technology to efficiently mineralize refractory contaminants from wastewater. In this work, 3D flower-like S-scheme N-Bi2O2CO3/g-C3N4 heterostructures were successfully constructed by hydrothermal method with the auxiliary of ionic liquids. The photocatalytic experiments show that the catalytic activity of heterojunction photocatalysts was significantly higher than that of bare g-C3N4 and N-Bi2O2CO3 for the degradation of two pollutants. NBOC/CN-2 shows the highest photocatalytic performance, and the degradation efficiency of sodium isobutyl xanthate (SIBX) on NBOC/CN-2 is 1.85 and 3 times that of bare g-C3N4 and Bi2O2CO3, respectively. The degradation efficiency of m-Cresol on NBOC/CN-2 is 8.34 and 6.93 times that of bare g-C3N4 and N-Bi2O2CO3, respectively. This significantly enhanced photocatalytic activity is attributed to the formation of flower-like heterojunctions, which can greatly increase the specific surface area and facilitate the separation and migration of photogenerated carriers. Total organic carbon (TOC) experiment proves that the two pollutants are effectively mineralized under the action of the prepared photocatalyst. The degradation path of m-Cresol degradation products was inferred based on the ion fragments. The capture experiment and Nitro-blue tetrazolium (NBT)-•O2- measurement show that superoxide radical plays a major role in photocatalytic degradation. The outstanding stability of the prepared flower-like heterojunction samples was examined by cyclic experiments. The S-scheme charge transfer mechanism has been proposed to explain the boosted activity of the flower-like heterojunction photocatalyst. This work provides a new idea for the design of efficient and stable g-C3N4-based photocatalyst for the photocatalytic degradation of refractory wastewater.