Visible-light-driven Research Articles

Fabrication of visible light responsive BaFe12O19/Ag/AgI composites with enhanced photocatalytic degradation of organic pollutants

A novel visible-light-driven (VLD) BaFe12O19/Ag/AgI photocatalysts were constructed through calcination and hydrothermal methods, in which BaFe12O19 of different mass ratios were introduced. The constructed Z-scheme heterojunction provided BaFe12O19/Ag/AgI composite catalytic with effective space carrier transport and higher redox ability. In particular, the as-prepared BaFe12O19/Ag/AgI degraded nearly 94% of 2- mercaptobenzothiazole within 30minutes of visible-light illumination, which was much superior to that of pure AgI (47%) and BaFe12O19 (3%). Moreover, BaFe12O19/Ag/AgI can be easily magnetically separated, so as to facilitate its efficient separation and recovery in practical application. Photocatalytic activity assays revealed that the as-synthesized BaFe12O19/Ag/AgI also exhibited good photodegradation capability towards Imidacloprid, Tetracycline and Carbamazepine. In particular, the complex had relatively high oxygen activation ability, and its photocatalytic H2O2 production performance was 1.29 times higher than that of the AgI monomer within 120minutes, thus realizing rapid water disinfection. Overall, the constructed efficient Z-scheme BaFe12O19/Ag/AgI photocatalysts provide a novel insight in sewage purification.

Visible light driven (VLD) reduced TiO2-x nanocatalysts designed by inorganic and organic reducing agent-mediated solvothermal methods for electrocatalytic and photocatalytic applications.

This work presents a comparative study on the structural, optical and electrochemical characteristics of visible light driven (VLD) reduced titanium dioxide (TiO2-x ) nanocatalysts synthesized via inorganic and organic synthetic routes. X-ray diffraction (XRD) patterns, Raman spectra and X-ray absorption fine structure (XAFS) analyses reflected anatase phase titania. Whereas, the quantitative EXAFS fit and XANES analysis revealed structural distortion due to the presence of oxygen and titanium vacancies with low valent Ti states in anatase lattices of certain nanocatalysts, which subsequently leads to better electrochemical and photocatalytic activities. Moreover, owing to the large surface area and mesoporous structures, the Mg-TiO2-x nanocatalysts exhibited enhanced water adsorption and ultimately increased overall water splitting with an OER overpotential equal to 420 mV vs. RHE at a current density of 10 mA cm-2 (Tafel slope = 62 mV dec-1), extended visible light absorbance, decreased photoluminescence (PL) intensity and increased carrier lifetime in comparison with commercial titania.

Synthesis of carbon quantum dot synthesized using spent coffee ground as a biomass exhibiting visible-light-driven antimicrobial activity against foodborne pathogens

The aim of this study was to synthesize carbon quantum dot (CQD) exhibiting visible-light-driven (VLD) antimicrobial activity using spent coffee ground (SCG) as biomass. SCG was used to synthesize CQD through microwave treatment. It was confirmed that typical CQD was synthesized well based on morphology (high resolution transmission electron microscopy), size distribution (dynamic light scattering), and chemical structure (X-ray photoelectron spectroscopy) analyses. VLD antimicrobial activities of CQD synthesized from SCG against Staphylococcus aureus and Escherichia coli O157:H7 were found to be increased as pH decreased. Photodynamic properties of CQDs such as fluorescence quantum yield (FLQY), band gap energy (Eg), and fluorescence lifetime as photodynamic properties of CQDs related to VLD antimicrobial activity did not show any significant changes according to pH change. However, as pH decreased, negative zeta potential (mV) values of CQD and pathogenic bacteria gradually decreased. As a result, it was confirmed that CQD uptake into pathogens was gradually increased due to a decrease in repulsive force between them. In addition, it was found that as pH decreased, activities of enzymes (superoxide dismutase and catalase) known to scavenge reactive oxygen species (ROS) in cells decreased. In the presence of CQD, when visible light was applied, the amount of ROS generated inside cells increased as pH decreased. Based on these results, CQD synthesized from SCG was combined with organic acid (malic acid) for practical application in fresh produce (apple surface) washing. It was confirmed that such combination had an excellent control effect against pathogenic bacteria, suggesting that this strategy could be effectively utilized in the food industry.

BaFe12O19/BiOBr S-scheme heterojunction magnetic nanosheets for high-efficiency photocatalytic degradation of 2-mercaptobenzothiazole

Visible-light-driven (VLD) BaFe12O19/BiOBr composite catalysts with different mass ratios of BaFe12O19 are prepared via hydrothermal and calcination method. The constructed S-type heterojunction enables BaFe12O19/BiOBr photocatalysts to perform effective space charge transfer and higher redox ability. Especially, the obtained BaFe12O19/BiOBr composites exhibited the high photocatalytic activity (95 %) to degrade 2-mercaptobenzothiazole (MBT) only after 3 min of visible light irradiation, which was much better than pure BaFe12O19 (10.6 %) and BiOBr (49 %). What's more, the BaFe12O19/BiOBr composites can be separated magnetically, thus achieving the practical significance of efficient separation and recovery. Photocatalytic activity experiments demonstrated that the prepared composites also showed good photocatalytic degradation performance towards Tetracycline hydrochloride (TC), Ciprofloxacin (CIP) and Eosin. Overall, the separable BaFe12O19/BiOBr composite photocatalysts will be promising candidate materials in sewage purification.

New insight into the visible-light-driven photoinduced electron transfer mechanism for ozone activation over defective sites of ceria for organic compounds destruction

Herein, we prepared CeO2 with varying concentrations of oxygen vacancies (Ov) and investigated the effects of the Ov concentration and photoinduced electron transfer (PET) on O3 activation under visible-light-driven (VLD) photocatalytic-ozonation (PO) for removal of oxalic acid (OA). Density functional theory calculations showed the formation of Ov reduced the bandgap of CeO2, leading to region around the Ce atom with a low adsorption energy barrier toward O3. Notably, no distinct linear correlation was found between the Ov concentration and VLD-PO activity. This implies that CeO2 with a lower amount of Ov (14.64%) exhibits better PET and higher photoexcited electron density than CeO2 with a relatively higher Ov (17.62%), suggesting that the PET properties of CeO2 are crucial for the Ov regeneration and O3 activation and conversion for OA removal. Electric energy per order (EEO) for VLD-PO using CeOx(700) was 6.94 kWh m−3 order−1. Additionally, bioassay experiments with Daphnia Magna showed toxicity reduction in the PO-treated effluent and continuous-flow experiments (CFEs) proved that VLD-PO could effectively remediate the toxic and refractory micropollutants containing water. The study findings can promote the application of PO systems in water treatment for treating organic pollutants.

Constructing AgBr/BiOBr@silkworm cocoons photocatalytic degradation and antibacterial material: Based on the excellent adsorption properties of silkworm cocoons

The silkworm cocoon (SC) possesses excellent adsorption performance due to the specific composite structure. Silk fibroin, the main component of SC, possesses lots of functional groups which are suitable for attachment of ligands, it plays an important role in the adsorption and chelation of metal ions, thus making SC a meaningful carrier. As a result, SC exhibits the best adsorption effect on Malachite green (MG), reaching 86.8% within 3 h in the present work. Additionally, AgBr/[email protected] visible light-driven (VLD) photocatalyst was successfully fabricated by ultrasound-assisted impregnation method with AgBr/BiOBr as a model and SC as a support. AgBr/[email protected] showed a remarkable photocatalytic degradation rate for Rhodamine B (Rh B, 98.52%), MG (80.08%) and Tetracycline (TC, 70.92%) under 120 min irradiation. Besides, it displayed superior activity in Staphylococcus aureus (S. aureus) disinfection, and the antibacterial efficiency above 99% upon 20 min of visible-light irradiation. The outstanding photocatalytic and antibacterial properties were mainly attributed to intimate contact and matched energy band positions between AgBr and BiOBr, which efficiently produce more active e--h+ pairs, and availably restrict the recombination of photogenerated carriers. This work could arouse an increasing interest in designing more SC-based photocatalysts for wastewater treatment.

Large-Area and Visible-Light-Driven Heterojunctions of In2O3/Graphene Built for ppb-Level Formaldehyde Detection at Room Temperature.

Achieving convenient and accurate detection of indoor ppb-level formaldehyde is an urgent requirement to ensure a healthy working and living environment for people. Herein, ultrasmall In2O3 nanorods and supramolecularly functionalized reduced graphene oxide are selected as hybrid components of visible-light-driven (VLD) heterojunctions to fabricate ppb-level formaldehyde (HCHO) gas sensors (named InAG sensors). Under 405 nm visible light illumination, the sensor exhibits an outstanding response toward ppb-level HCHO at room temperature, including the ultralow practical limit of detection (pLOD) of 5 ppb, high response (Ra/Rg = 2.4, 500 ppb), relatively short response/recovery time (119 s/179 s, 500 ppb), high selectivity, and long-term stability. The ultrasensitive room temperature HCHO-sensing property is derived from visible-light-driven and large-area heterojunctions between ultrasmall In2O3 nanorods and supramolecularly functionalized graphene nanosheets. The performance of the actual detection toward HCHO is evaluated in a 3 m3 test chamber, confirming the practicability and reliability of the InAG sensor. This work provides an effective strategy for the development of low-power-consumption ppb-level gas sensors.

Efficient photocatalytic degradation of high-concentration moxifloxacin over dodecyl benzene sulfonate modified graphitic carbon nitride: Enhanced photogenerated charge separation and pollutant enrichment

Photocatalysis technology has been proved to be a promising strategy to eliminate antibiotic pollution from wastewater, in spite of arduous challenges such as insufficient utilization of sunlight, high recombination of photogenerated charges, low efficiency of high-concentration antibiotics, and infrequent investigation on new antibiotics. Herein, we synthesized a visible-light-driven (VLD) photocatalyst by modifying dodecyl benzene sulfonate (DBS) onto graphitic carbon nitride nanosheet (CNNS), and studied its photocatalytic performance for removing high-concentration moxifloxacin (MOX), a fourth-generation quinolone antibiotic. Compared with other studies (Table S1), this catalyst broke through the bottleneck of degradation of high concentration MOX, which could remove 100 mg L−1 MOX under 30 min of irradiation. The hydrophobic dodecyl benzene group and the formed sulfonyl group with strong electron-withdrawing property were beneficial to boost the MOX enrichment from the bulk solution and suppress the recombination of photogenerated charges. The effect of pH value, MOX concentration and photocatalyst dosage was also studied in order to explore the best photocatalytic reaction condition. The superior photocatalytic durability and practical application prospects of DBS/CNNS were also demonstrated. By revealing the band structure of the DBS/CNNS hybrid, as well as the active species and the intermediate products generated in the photocatalytic process, a plausible photocatalytic mechanism was proposed. This study indicates that the DBS/CNNS hybrid is a potential VLD photocatalyst for efficient elimination of high-concentration antibiotics in wastewater.

Dual-functional Mo2C quantum dots enriched N-doped graphitic carbon layers in advanced oxidation processes (AOPs)

Advanced oxidation processes (AOPs) are reckoned effective for removing persistent and recalcitrant pollutants by reactive oxygen species (ROSs), including hydroxyl radicals (•OH), sulfate radicals (SO4•-), and superoxide radicals (•O2-), as well as singlet oxygen (1O2). In this work, the Mo2C quantum dots enriched N-doped graphitic carbon layers (Mo2C QDs/NGCLs) were constructed via a facile two-step methodology. Interestingly, the Mo2C QDs/NGCLs acted as a highly efficient cocatalyst and/or catalyst simultaneously in AOPs, in particular visible-light-driven (VLD) Fenton and VLD PMS activation. In the hydroxyl radical-based AOPs (•OH-AOPs), it exhibited a remarkable removal efficiency for a range of aromatic organic pollutants, including rhodamine B (RhB) (99.9 %), phenol (90 %), benzophenone-3 (BZP) (83 %), methyl orange (MO) (58 %), methyl blue (MB) (89 %), ibuprofen (IBU) (100 %), and carbamazepine (CBZ) (50 %). Sulfate radicals-based AOPs (SR-AOPs) effectively degrade RhB (72 %), MO (83 %), IBU (70 %), and BZP (100 %). Thus, the present findings confirmed the potential of transition metal carbides for AOP applications and established a solid theoretical and technical basis for further research.

Semiconductors Application Forms and Doping Benefits to Wastewater Treatment: A Comparison of TiO2, WO3, and g-C3N4

Photocatalysis has been vastly applied for the removal of contaminants of emerging concern (CECs) and other micropollutants, with the aim of future water reclamation. As a process based upon photon irradiation, materials that may be activated through natural light sources are highly pursued, to facilitate their application and reduce costs. TiO2 is a reference material, and it has been greatly optimized. However, in its typical configuration, it is known to be mainly active under ultraviolet radiation. Thus, multiple alternative visible light driven (VLD) materials have been intensively studied recently. WO3 and g-C3N4 are currently attractive VLD catalysts, with WO3 possessing similarities with TiO2 as a metal oxide, allowing correlations between the knowledge regarding the reference catalyst, and g-C3N4 having an interesting and distinct non-metallic polymeric structure with the benefit of easy production. In this review, recent developments towards CECs degradation in TiO2 based photocatalysis are discussed, as reference catalyst, alongside the selected alternative materials, WO3 and g-C3N4. The aim here is to evaluate the different techniques more commonly explored to enhance catalyst photo-activity, specifically doping with multiple elements and the formation of composite materials. Moreover, the possible combination of photocatalysis and ozonation is also explored, as a promising route to potentialize their individual efficiencies and overcome typical drawbacks.

Electro-assisted heterogeneous activation of peroxymonosulfate by g-C3N4 under visible light irradiation for tetracycline degradation and its mechanism

In the current study, to promote peroxymonosulfate (PMS) activation efficiency of visible-light-driven (VLD) photocatalysis of g-C3N4 (CN) (VLD/CN/PMS) process, electrochemical (EC) process was introduced to assist VLD/CN/PMS process to construct a coupled process (EC + VLD/CN/PMS). Compared to single VLD/CN/PMS, EC assisting CN activating PMS (EC/CN/PMS), and CN activating PMS (CN/PMS) process, EC + VLD/CN/PMS process exhibited an apparently boosted PMS activation efficiency toward TC degradation due to the interaction effect of EC and VLD photocatalysis process promoting the PMS adsorption on CN surface. It shows that surface radicals and electron-transfer mechanism in the EC + VLD/CN/PMS process made the dominant contribution to TC degradation, which was evidenced by the quenching experimental results, EPR test, and electrochemical analysis. Noticeably, the EC + VLD/CN/PMS process exhibited strong resistance to the coexisting anions even with a high concentration (200 mM) in water, as the PMS adsorption capacity was little affected by those anions, with wide pH adaptability (3–11), high stability, and universal applicability for various organics. In addition, based on the detected intermediates and density functional theory (DFT) calculations, the pathways of TC degradation were revealed in detail. In brief, EC + VLD/CN/PMS process was proved to be a reliable technology for antibiotic pollutant removal.

Red Phosphorus Nanodot-Decorated Polymeric Carbon Nitride Nanotubes for Visible-Light-Driven Photocatalytic Bacterial Inactivation

Pathogenic microorganisms related to infectious diseases severely threaten human health, and visible-light-driven (VLD) photocatalysis is a promising strategy for mitigating microbial-induced health crises. In this work, a superior and effective VLD photocatalyst comprising a red phosphorus nanodot-modified one-dimensional carbon nitride nanotube (RP-CN) heterostructure was synthesized with a simple chemical vapor deposition method and used for bacterial inactivation. The optimized RP (40)-CN rapidly and completely destroyed Escherichia coli and Staphylococcus aureus (107 CFU mL–1) within 25 and 30 min under irradiation with a white LED, respectively. The efficient photocatalytic activity was attributed to the fact that the matching work function in the CN-RP heterojunction promotes the charge migration/separation that occurs at the CN and RP interface and the broad absorption spectra by RP loading. Additional unpaired photoelectrons reacted with water to generate •O2– radicals and H2O2 for efficient bacterial cell inactivation. The present study highlights the design of nanostructured photocatalysts with wide spectral responses for efficient energy conversion and wide antibacterial scope.

Water hyacinth powder -assisted preparation of defects-rich and flower-like BiOI/Bi5O7I heterojunctions with excellent visible light photocatalytic activity

Flower-like BiOI/Bi5O7I type-II heterojunctions with oxygen vacancies (OVs) have been in-situ constructed by calcining flower-like BiOI obtained by a hydrothermal tactic with the assistance of water hyacinth powder (WHP). The photocatalysts were characterized by specific surface area, X-ray diffraction pattern (XRD), scanning electron microscope (SEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and electron spin resonance spectroscopy (ESR). The efficient photogenerated carriers separation of the photocatalysts was demonstrated by surface photovoltage spectrum (SPS) and photocurrent experiments. The trapping experiments determine that h+ and •O2− are the main active free radicals in the visible light driven (VLD) photocatalytic system. Low-temperature ESR proves the existence of OVs, which greatly promotes the photocatalytic activity. When the mass ratio of WHP/Bi(NO3)3•5H2O is 8%, the prepared BiOI/Bi5O7I photocatalyst represents the best photocatalytic performance under visible light irradiation. The removal rate constant of Rhodamine B (RhB) and phenol over the 8% samples is 0.022 min−1 and 0.24 h−1, which is 27 and 3-fold of that over the 0% sample, respectively. The effective transfer and efficient utilization of photogenerated e−/h+ and the presence of OVs jointly improve the activity of the BiOI/Bi5O7I composite photocatalyst. This work develops an effective strategy for synthesis of visible light driven photocatalytic materials by taking advantage of biomass.

Ultrasensitive photoelectrochemical platform with micro-emulsion-based p-type hollow silver iodide enabled by low solubility product (K sp) for H2S sensing

Since visible-light (VL) accounting for massive solar radiation energy, a large amount of attention has been paid to the development of highly efficient visible-light-driven (VLD) semiconductor materials. However, despite recent efforts to construct VL active material, hollow structure-based silver iodide (AgI) with appropriate band gap and a large surface area are limited because of lack of a proper synthesis method. Herein, hollow AgI with p-type semiconductor behavior is constructed on the basis of micro-emulsion strategy, which enables admirable cathode photoelectrochemical (PEC) response. The as-prepared hollow AgI is applied to fabricate the PEC sensing platform and reveals a low limit of detection of 0.04 fM and a wide dynamic range up to 5 orders of magnitude toward H2S. The PEC sensing mechanism is supposed to the ‘signal-off’ pattern on account of the ultralow solubility product (K sp) of Ag2S, derived from the precipitation reaction due to the high affinity between sulfide ion and Ag+. Besides, the hollow structure of AgI provides sufficient surface area for in situ producing Ag2S that serves as recombination center of carrier, thus causing the efficient quenching of photocurrent signals. This work broadens the horizon of structuring VLD semiconductor nanomaterials and K sp-based H2S sensing.

Hydrothermal fabrication and characterization of novel CeO2/PbWO4 nanocomposite for enhanced visible-light photocatalytic performance

In this revision, a series of novel visible-light-driven (VLD) CeO2/PbWO4 nanocomposites (NCs) were effectively fabricated by facile hydrothermal preparation way. The UV–Vis absorption spectra exposed that CeO2 NPs prolonged the adsorption edge of the CeO2/PbWO4 composite to the extensive visible region, which allied to decreases of the bandgap. As-prepared CeO2/PbWO4 NCs revealed superior photocatalytic action under visible-light and could degrade the Methylene Blue (MB) dye solution in 140 min. The photodegradation efficacy of CeO2/PbWO4 NCs was improved catalytic activity, which is around 1.45 and 2.7 times that of CeO2 and PbWO4 nanoparticles (NPs) individually. Besides, the CeO2/PbWO4 catalysts display notable stability and reusability performance in four succeeding cycles. The development in the photocatalytic enactment of combined CeO2/PbWO4 nanocomposite could be recognized not only to the sturdy visible-light absorption responses and separating the photoexcited electron–hole pairs. Also, the plausibly systematic illumination of charge transference and exploitation of reactive species for superior photocatalytic action in visible-light have been discussed. It is projected that the CeO2/PbWO4 NCs could be used as effective photocatalysts for promising applications for environmental wastewater refinement.

Designing heterointerface in BiOBr/g-C3N4 photocatalyst to enhance visible-light-driven photocatalytic performance in water purification

A rapid recombination of photo-generated electrons and holes is the intrinsic defect in graphitic carbon nitride (g-C 3 N 4 )-based photocatalysts. Inspired by natural photosynthesis, an artificially synthesized Z-scheme photocatalyst can efficaciously restrain the recombination of photogenerated electron-hole pairs and enhance the photoabsorption ability. Herein, a series of novel visible-light-driven (VLD) solid-state Z-scheme BiOBr/g-C 3 N 4 heterostructured photocatalysts were successfully synthesized via a facile in-situ oxidation method which enabled the BiOBr nanosheets to grow on the surface of g-C 3 N 4 . The introduction of BiOBr on g-C 3 N 4 to constitute a Z-scheme heterojunction system can effectively broaden the light absorption range and promote the separation of photo-generated electron-hole pairs. Besides, the Z-scheme mechanism proved by active species trapping experiments led to the persistence of photoinduced electrons in the CB of g-C 3 N 4 while holes in the VB of BiOBr, thus ensuring the high redox ability of the charge carriers. Notably, the BC12% sample exhibited the optimized photocatalytic activity in which the RhB molecules were decomposed within 20 min under visible light irradiation, achieving 3.3- and 2.3-fold improvement than the bare g-C 3 N 4 and pristine BiOBr, respectively. Meanwhile, the BC12% sample still revealed the superiority in both photodegrading MO and photoreducing Cr(VI). As an original strategy to obtain samples with highly dispersed heterointerface, this work could provide a facile route for the construction of g-C 3 N 4 -based solid-state Z-scheme heterojunction and very promising for practical application. • Novel Z-scheme BiOBr/g-C 3 N 4 heterojunctions were synthesized via hydrolysis method. • The highly dispersed heterointerface accelerated charge carriers transfer. • The massive unshifted charge carriers with higher redox ability were realized. • The photoreducibility for Cr(VI) was largely enhanced on BiOBr/g-C 3 N 4 composites.

Synthesis of a novel ternary (g-C3N4 nanosheets loaded with Mo doped ZnOnanoparticles) nanocomposite for superior photocatalytic and antibacterial applications

This article reports the synthesis of a novel ternary Visible-Light-Driven (VLD) photocatalyst and antibacterial agent. The two-dimensional graphitic carbon nitride nanosheets (g-C3N4 NSs) and 7% molybdenum doped zinc oxide nanoparticles (Mo doped ZnO NPs) were used for the synthesis of the 65% g-C3N4 hybridized with 7% Mo doped ZnO novel ternary nanocomposite (Mo doped ZnO/g-C3N4 ternary NC). The synthesis process, as well as the structures, morphologies, photocatalytic and antibacterial properties of the synthesized ternary NC and constituents, were investigated by using several spectroscopic and microscopic techniques. It was revealed through the Transmission Electron Microscopy (TEM) characterization of the synthesized NC that the Mo doped ZnO NPs were found uniformly embedded upon the well-stacked g-C3N4NSs. It was further discovered by the bandgap analysis that the light absorbance ability of the ternary NC exists in the visible region of the light spectrum. The photocatalytic degradation of the methylene blue (MB) by the use of novel ternary NC in an aqueous medium was analyzed while using Ultra Violet-Visible (UV-Visible) spectroscopy. Trapping experiments of active species during the photodegradation and Electron Spin Resonance (ESR) experiment revealed that the superoxide and hydroxyl radicals were the leading species liable for MB deterioration. The ternary NC exhibited superior photocatalytic performance as compared with binary doped or hybridized nanomaterials (NMs) and mono photocatalysts due to the facility of effective migration and separation of the charge carriers across the (Mo doped ZnO NPs)/g-C3N4 NSs interface of the heterojunction. The increased generation of the reactive oxygen species (ROS), O2−, and •OH radicals the photogenerated charge carriers within the Mo doped ZnO/g-C3N4 NC were found responsible for its enhanced antibacterial performance.

Effect of amino acid-derived nitrogen and/or sulfur doping on the visible-light-driven antimicrobial activity of carbon quantum dots: A comparative study

• Un-doped CQD (C-CQD), N doped CQD (N-CQD), and NS doped CQD were synthesized with malic acid, alanine, and cysteine. • N and/or S doping lowered the band gap energy, making CQD have the visible-light-driven (VLD) antimicrobial activity. • VLD antimicrobial activity increases as the ratio of S decreases during N and S doping. • N-CQD had greater specific surface area, the fluorescence quantum yield and photoluminescence lifetime values than NS-CQD. The purpose of this study was to investigate the effects of nitrogen and sulfur derived from amino acids on the visible-light-driven (VLD) antimicrobial activity of carbon quantum dots (CQDs) and to establish an optimal doping form. Various CQDs were synthesized by combining malic acid as a carbon source, alanine containing N, and cysteine containing N and S through microwave heating. The results showed that the VLD antimicrobial activity of the CQD against Gram-positive ( Staphylococcus aureus and Listeria monocytogenes ) and Gram-negative pathogens ( Escherichia coli O157:H7 and Salmonella Typhimurium) was improved by N and/or S doping, which increased as the ratio of S decreased. The doping of N and/or S made CQDs have a lower band gap energy, and CQD doped with only N (N-CQDs) exhibited greater specific surface area and fluorescence quantum yields (FLQYs), and longer photoluminescence (PL) lifetimes than CQD doped with N and S (NS-CQDs) even though NS-CQD and N-CQD had similar hand gap energies. Based on these results, the mechanism by which the VLD antimicrobial activity of CQD changes by doping was discussed. Furthermore, this study suggests that for CQD synthesis using food by-products, the more amino acids that can induce the doping of N and/or S, wherein the smaller ratio of S containing amino acids, the better VLD antimicrobial activity the synthesized CQD will have.

N-doped graphitic C3N4 nanosheets decorated with CoP nanoparticles: A highly efficient activator in singlet oxygen dominated visible-light-driven peroxymonosulfate activation for degradation of pharmaceuticals and personal care products

CoP nanoparticle-loaded N-doped graphitic C3N4 nanosheets (CoP/N-g-C3N4) were fabricated via a facile three-step method to degrade pharmaceuticals and personal care products (PPCPs) via a visible-light-driven (VLD) peroxymonosulfate (PMS) activation system. 2 ppm carbamazepine (CBZ) can be removed completely within 10 min by the VLD-PMS system with a kinetic constant of k = 0.29128 min−1, as 25.8 times compared to that under dark conditions (k = 0.01128 min−1). The experimental and theoretical results showed that the doped graphitic N atoms could modulate the electronic properties of the g-C3N4 nanosheets. Subsequently, the Density Functional Theory (DFT) explained that CoP showed preference to bonding with the nitrogen atoms involved in the newly formed N˭N bond, and the Co‒N bond dramatically enhanced the transfer of photo-generated electrons from the N-g-C3N4 nanosheets. Electron paramagnetic resonance (EPR) tests show that singlet oxygen (1O2) plays a leading role in this case. Moreover, PMS molecules are also tended to be absorbed onto the electron-deficient carbon atoms near the newly formed N˭N bonds for PMS reduction, synergistically enhancing the degradation efficiency for CBZ and benzophenone-3 (BZP). The newly established VLD-PMS activation system was shown to treat the actual sewage in Hong Kong sewage treatment plants (STPs) very well. This work supplements the fundamental theory of radical and non-radical pathways in the sulfate radical (SO4•-)-based advanced oxidation process (SR-AOP) for environmental cleanup purposes.

The role of g-C3N4 in round-the-clock photocatalysis for POME

The main drawback of conventional palm oil mill effluent (POME) treatment is that the process is time and space-consuming. Besides, the treatment produces highly polluted wastewater that pollutes the environment if discharged directly. Photocatalytic process has significant potential to degrade recalcitrant organic pollutants and has recently attracted tremendous attention. However, current approaches mainly focus on visible light condition, which is still an ineffective treatment for POME. In this study, POME was successfully degraded using graphitic carbon nitride (g-C3N4) photocatalyst synthesised by calcination. The prepared photocatalyst was characterised by ultraviolet-visible diffuse reflectance (UV-Vis DRS) spectroscopy and scanning electron microscopy (SEM). The SEM results revealed the morphology of g-C3N4 photocatalyst. g-C3N4 could act as a visible-light-driven (VLD) photocatalyst with the highest photocatalytic efficiency of 71% under visible light. The present work highlights the potential of g-C3N4 towards the degradation of POME under visible light and dark condition. The highly enhanced photocatalytic performance is attributed to g-C3N4, but it does not work well in round-the-clock photocatalysis. However, g-C3N4 can work as the band alignment to drive separate photogenerated charge carriers, leading to effective photocatalytic degradation. g-C3N4 photocatalyst may be considered as an ideal candidate for treating POME.