Enhanced Photocatalytic Degradation of Environmental Pollutants under Visible Irradiation by a Composite Coating

Zwitterionic MOF-embedded alginate beads with polydopamine surface functionalization for efficient doxycycline removal: Optimization and mechanistic study

The adsorptive removal of amphoteric antibiotics like doxycycline (DOX) is a difficult task because of the electrostatic repulsion between these amphoteric molecules and adsorbents. For this purpose, a zwitter adsorbent was fabricated by incorporating zwitter ZIF-67/MIL-88A binary MOF into the matrix of alginate (Alg); in addition, the surface of the beads was modified by polydopamine (PDA). The batch experiments implied the super-high adsorption efficacy of ZIF-67/MIL-88A@Alg@PDA toward DOX attained 384.61 ± 5.08 mg/g at a neutral pH medium, 25 °C, and using 0.02 g. The isotherm analysis implied the physisorption of DOX onto ZIF-67/MIL-88A@Alg@PDA, while the kinetic analysis denoted the chemisorption of DOX. The results of XPS, Zeta potential, and Lab experiments identified the types of physical and chemical interactions between ZIF-67/MIL-88A@Alg@PDA and DOX. The durability of the ZIF-67/MIL-88A@Alg@PDA beads was inspected by the recycling test, clarifying that the DOX adsorption aptitude declined by 12.22 mg/g. In addition, the measured leaching concentrations of cobalt and iron from leaching test were 0.008 and 0.098 mg/L. The ionic strength of ZIF-67/MIL-88A@Alg@PDA, implying an enhancement in the DOX removal (%) from 83.51 to 93.50 % by raising the NaCl concentration from 0.2 to 1.0 mol/L. Therefore, our study could provide a simple procedure to overcome the electrostatic repulsion that retard the adsorption process of the amphoteric drugs onto charged adsorbents with positive or negative charges. Additionally, this procedure could also generate an electrostatic interaction between the zwitter adsorbents and the amphoteric drugs at specific pH media when they are in a zwitterionic nature.

In vitro analyses of cerium oxide nanoparticles in degrading anthracene/fluorene and revealing the antibiofilm activity against bacteria and fungi

A sol-gel method was used to synthesize the cerium dioxide nanoparticles. The nanoparticles formed were then characterized with UV-visible spectrophotometry, Fourier Transform Infrared Spectrophotometer (FTIR), SEM-EDAX, XRD, and Dynamic Light Scattering (DLS). The UV-visible absorbance at 282 nm and characteristic peak at 600-4000 cm-1 provided insight into the formation of cerium dioxide nanoparticles using a chemical method. SEM analysis and EDAX analysis confirmed nanoparticle formation and elements within the nanoparticles based on their irregular morphology. The hydrodynamic size obtained from the DLS analysis was 178.4 nm and the polydispersity was 0.275 nm. Furthermore, XRD results confirmed the crystalline nature of cerium dioxide nanoparticles. Using batch adsorption as a method, the effect of concentration of Polycyclic Aromatic Hydrocarbons (PAH), adsorbent concentration, pH, and irradiation source was investigated. Under UV light conditions, 10 μg/mL cerium dioxide nanoparticle at pH 5 degraded 2 μg/mL of PAH (anthracene and fluorene). Consequently, the synthesized cerium dioxide nanoparticles were effective photocatalysts. For anthracene and fluorene, kinetic studies showed the degradation process followed pseudo-second-order kinetics and Freundlich isotherms. Cerium oxide also exhibited significant antimicrobial and antibiofilm activity against bacteria and fungi. As a result, the cerium dioxide nanoparticle has proved to be a highly effective photocatalytic tool for the degradation of PAHs and exhibits strong antimicrobial activity.

Photocatalytic and Photothermal Antimicrobial Mussel-Inspired Nanocomposites for Biomedical Applications

Bacterial infection has traditionally been treated with antibiotics, but their overuse is leading to the development of antibiotic resistance. This may be mitigated by alternative approaches to prevent or treat bacterial infections without utilization of antibiotics. Among the alternatives is the use of photo-responsive antimicrobial nanoparticles and/or nanocomposites, which present unique properties activated by light. In this study, we explored the combined use of titanium oxide and polydopamine to create nanoparticles with photocatalytic and photothermal antibacterial properties triggered by visible or near-infrared light. Furthermore, as a proof-of-concept, these photo-responsive nanoparticles were combined with mussel-inspired catechol-modified hyaluronic acid hydrogels to form novel light-driven antibacterial nanocomposites. The materials were challenged with models of Gram-negative and Gram-positive bacteria. For visible light, the average percentage killed (PK) was 94.6 for E. coli and 92.3 for S. aureus. For near-infrared light, PK for E. coli reported 52.8 and 99.2 for S. aureus. These results confirm the exciting potential of these nanocomposites to prevent the development of antibiotic resistance and also to open the door for further studies to optimize their composition in order to increase their bactericidal efficacy for biomedical applications.

Daylight Photoactive TiO2 Sol-Gel Nanoparticles: Sustainable Environmental Contribution

Visible-light-photoactive titania micro- or nanoparticles excel in a wide range of industrial areas, particularly in environmental remediation. The sol-gel methodology is one pivotal technique which has been successfully used to synthesize either crystalline and amorphous TiO₂ micro- and nanoparticles due to its outstanding chemical simplicity and versatility, along with the green chemistry approach. This short review aims to collect and discuss the most recent developments in visible-light-photoactive titania-based nanoparticles in the environmental remediation area. Titania co-doping, titania composite design, and, recently, amorphous networks have been the most used strategies to address this goal. Finally, a prediction regarding the future of these fields is given.

Direct Z-scheme P-TiO2/g-C3N4 heterojunction for the photocatalytic degradation of sulfa antibiotics

The construction of direct Z-scheme heterojunctions with high photocatalytic degradation ability is important for wastewater treatment, but there are still many unsolved challenges. In this article, we report the fabrication of a Z-scheme P-TiO₂/g-C₃N₄ (CNPT-X) heterostructure by the calcination method. Under simulated sunlight, CNPT-X composites are found to show excellent degradation performance against sulfonamide antibiotics sulfadiazine (SD), sulfamethazine (SM2), sulfamonomethoxine (SMM), and sulfamethoxazole (SMZ). CNPT-3 (400 mg L^-1) can be used to degrade four sulfa antibiotics within 90 min, with a degradation rate as high as 99%, which is higher than that for P-TiO₂ and g-C₃N₄ alone. The internal electron transfer paths and mechanisms for the composites are revealed by ESR radical detection experiments, XPS energy spectrum shifts, valence band positions and active material quenching experiments. Furthermore, the degradation products are analyzed by GC-MS, and four possible degradation pathways for sulfonamide pollutants are proposed. This photocatalyst provides new insights into the fundamental aspects of the photocatalytic degradation mechanism for composite pollutants, as well as new ideas for practical environmental applications.

Enhanced photocatalytic activity of nano-silica/copper plasmon by aminofunctional silane for dye pollutant degradation

The synthesis of silica gel nanostructures and loading it with copper specie via a hydrothermal process were performed. The sample is treated with an amino-functional reagent 3-aminopropyl triethoxysilane (APTES). The products were characterized by X-ray diffraction (XRD), FT-IR, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), TGA/DSC measurements, and X-ray photoelectron spectroscopy (XPS). The photocatalytic activities of the nanostructures were studied for degradation of methylene blue dye (as a classic dye contaminant) in aqueous solution utilizing visible light source. The results displayed that the sample treated with APTES is much more effective in photocatalytic degradation of methylene blue. This modified catalyst could eliminate methylene blue dye (50 mL, 18 µg mL^-1) within 60 min under visible light. The degradation efficiency was increased by shortening the degradation time to 30 min in the alkaline medium. The pseudo-first-order model well describes the kinetics of the reaction.

Theoretical and experimental studies on photocatalytic removal of methylene blue (MetB) from aqueous solution using oyster shell synthesized CaO nanoparticles (CaONP-O)

The development of technologies for the removal of dye from aqueous solution is most desirable if the end product is relatively green (i.e., environmentally friendly). Photodegradation (as one of such technology) and photolysis (without the catalyst) was applied to investigate the role of sol-gel synthesized calcium oxide nanoparticle (using the oyster shell as the precursor). The results obtained gave substantial evidence that calcium oxide nanoparticles catalyzed the degradation of the methylene blue dye up to a maximum percentage of 98 % removal. Degradation efficiency displayed a strong dependency on time, initial dye concentration, catalyst load, pH, and ionic strength. Chi-square and sum of square error analysis indicated that the photodegradation kinetics fitted the Langmuir-Hinshelwood, first order, and pseudo first-order models best. The half-life of the dye was significantly reduced from hours to minutes due to photocatalysis. Quantum chemical calculations indicated that the degradation proceeded through adsorption, deformation/degradation, and desorption through the chloride end of the molecule linked to the calcium active center of the catalyst. Results from Fukui functions and molecular descriptors analysis confirmed the mechanism of photocatalysis.

Modeling RSM of photocatalytic treatment of Acid Red 18 pollutant using ZnO–Cr nano-photocatalyst, kinetic studies, and energy management

The ZnO–Cr nano-photocatalyst was synthesized using a microwave-assisted solution combustion method and applied for the photodegradation of the organic pollutant Acid Red 18 (AR18). The synthesized nano-photocatalyst was characterized by XRD, FESEM, EDX, and FTIR methods. To reach the optimal condition of the treatment, the response surface methodology was used in the central composite design model. The amount of nano-photocatalyst, pH of the solution, and initial concentration of the pollutant were optimized. The polynomial 3-degree model was fitted to the photodegradation data, and the correlation coefficients of the model showed an interaction between the parameters. Optimization of the polynomial model for pollutant treatment was investigated under the same conditions, and the comparison of the observed and predicted treatment models showed a low difference in decolorization. The intermediates were identified by liquid chromatography/mass spectrometry. A kinetic study showed that the first-order kinetic constant for the degradation of pollutant concentrations from 10 to 30 mg L−1 changed from 0.0178 to 0.0058 min–1. Finally, economic evaluation and energy management of the process showed that the decolorization process was more economical at low pollutant concentrations.

High-quality syngas production: The green and efficient utilization of waste tire and waste heat from the steelmaking converter process

This study proposes a new technology in which waste tire powders are injected into a converter vaporization cooling flue for gas recovery via pyrolysis using high-temperature waste heat. The higher temperature pyrolysis behavior of waste tire powder under different heating rates was investigated using a TG-MS technique. A drop tube furnace was used to simulate the converter vaporization cooling flue to investigate the effect of high temperatures on waste tire powder pyrolysis. The results indicated that secondary pyrolysis occurred above 900 °C with low weight and weight loss rates, which were considerably lower than those observed in the thermal degradation stage. The main gaseous products formed were CO, CO₂, H₂, CH₄, and H₂O. The drop tube furnace experimental results indicated that high temperatures can facilitate the degradation of waste tire powder to generate more H₂ and CO and improve the low heating values. At 1200 °C, the H₂ and CO contents were approximately 19.60% and 4.90%, respectively. The low heating value was 29.64 MJ/Nm³. The char yield was in the range of 32.67%-37.33%; the fixed carbon content increased from 79.63% to 84.75%. The results provide preliminary verification of the feasibility of injecting waste tire powders into a converter vaporization cooling flue for gas recovery.

Greatly enhanced oxidative activity of δ-MnO2 to degrade organic pollutants driven by dominantly exposed {-111} facets

The reactivity of oxidizing materials is highly related to the exposed crystal facets. Herein, δ-MnO₂ with different exposure facets were synthesized and the oxidative activities of the as-prepared materials were evaluated by degrading phenol in water without light. The degradation rate of phenol by δ-MnO₂-{-111} was significantly higher than that by δ-MnO₂-{001}. δ-MnO₂-{-111} also displayed high degradation efficiency to a variety of other organic pollutants, such as ciprofloxacin, bisphenol A, 3-chlorophenol and sulfadiazine. Comprehensive characterization and theoretical calculation verified that the {-111} facet had high density of Mn³⁺, thus displaying enhanced direct oxidative capacity to degrade organic pollutants. In addition, the dominant {-111} facet promoted adsorption/activation of O₂, thus favored the generation of superoxide radical (O₂^•-), which actively participated in the degradation of pollutants. The phenol degradation kinetics could be divided into two distinct phases: the rapid phase (k1_obs = 0.468 min^-1) induced by Mn³⁺ and the slower phase (k2_obs = 0.048 min^-1) dominated by O₂^•-. The synergistically promoted non-radical and radical based reactions resulted in greatly enhanced the oxidative activity of the δ-MnO₂-{-111}. These findings deepen the understanding of facet-dependent oxidative performance of materials and provided valuable insights into the possible practical application of δ-MnO₂ for water purification.

Dynamic monitoring and regulation of pentachlorophenol photodegradation process by chemiluminescence and TiO2/PDA

Pentachlorophenol (PCP), a highly toxic halogenated aromatic compound, and its direct photolysis or TiO₂ photocatalysis may generate toxic intermediates and induce secondary pollution in the environment. It is urgently needed to design a strategy to inhibit the toxic intermediates in the photodegradation of PCP. To achieve this, polydopamine (PDA), a non-toxic substance, modified TiO₂ (P25/PDA) nanoparticles were synthesized and used to improve the PCP photodegradation process. The dynamic tracking of toxic intermediates tetrachloro-1,4-benzoquinone (TCBQ) and trichlorohydroxy-1,4-benzoquinone (OH-TrCBQ) produced in the PCP photodegradation process were obtained by continuous flow chemiluminescence. Combined with reactive oxygen species (ROS) measurements, P25/PDA could approximatively depress 70 % TCBQ and 40 % OH-TrCBQ generation through the regulation of ROS especially the generation of a fairly large amount of H₂O₂ (about 30 μM) and O₂^- (about 20 μM) on the surface of the P25/PDA. The toxicity evaluation showed that the photodegradation of PCP by P25/PDA was a safer and green approach. Therefore, it was instructive to inhibit the formation of highly toxic intermediates in the photodegradation of environmental contaminants by regulating the ROS generated on the surface of the photocatalysts.

Enhanced photocatalytic destruction of pollutants by surface W vacancies in VW-Bi2WO6 under visible light

W vacancies containing Bi₂WO₆ (V_W-Bi₂WO₆) was synthesized by a reductant-involved hydrothermal process. The photoactivity of Bi₂WO₆ was enhanced by 3.3 times and the TOC removal rate increased from 38.3% to 64.7% after the introduction of surface W vacancies. Positron annihilation spectrometry (PAS), XPS, Raman spectra and other characterization results indicated that W vacancies existed on the catalyst surface. The surface W vacancies were proved to widen the band gap and negatively shift CB edge to produce more O₂^•- and photoexcited holes at catalyst surface, as confirmed by ESR and radicals trapping experiments. Further, according to the results of pyridine adsorbed FTIR and Zeta potentials, the enhanced interaction between pollutants and V_W-Bi₂WO₆ was confirmed. As a result, the active species produced at surface were able to be accelerated to directly react with organic pollutants, leading to the highly efficient degradation and mineralization of pollutants in water.

Efficient SO2 Removal and Highly Synergistic H2O2 Production Based on a Novel Dual-Function Photoelectrocatalytic System

The direct conversion of SO₂ to SO₃ is rather difficult for flue gas desulfurization due to its inert dynamic with high reaction activation energy, and the absorption by wet limestone-gypsum also needs the forced oxidation of O₂ to oxidize sulfite to sulfate, which is necessary for additional aeration. Here, we propose a method to remove SO₂ with highly synergistic H₂O₂ production based on a novel dual-function photoelectrocatalytic (PEC) system in which the jointed spontaneous reaction of desulfurization and H₂O₂ production was integrated instead of nonspontaneous reaction of O₂ to H₂O₂. SO₂ was absorbed by alkali liquor then oxidized quickly into SO₄^2- by a nanorod α-Fe₂O₃ photoanode, which possessed high alkali corrosion resistance and electron transport properties. H₂O₂ was produced simultaneously in the cathode chamber on a gas diffusion electrode and was remarkably boosted by the conversion reaction of SO₃^2- to SO₄^2- in the anode chamber in which the released chemical energy was effectively used to increase H₂O₂. The photocurrent density increased by 40% up to 1.2 mA·cm^-2, and the H₂O₂ evolution rate achieved 58.8 μmol·L^-1·h^-1·cm^-2 with the synergistic treatment of SO₂, which is about five times than that without SO₂. This proposed PEC cell system offers a cost-effective and environmental-benign approach for dual purpose of flue gas desulfurization and simultaneous high-valued H₂O₂ production.

Catalytic degradation of ciprofloxacin by a visible-light-assisted peroxymonosulfate activation system: Performance and mechanism

Peroxymonosulfate (PMS) is extensively used as an oxidant to develop the sulfate radical-based advanced oxidation processes in the decontamination of organic pollutants and various PMS activation methods have been explored. Visible-light-assisted PMS activation to construct a Fenton-like process has shown a great potential for pollution control. In our work, BiVO₄ nanosheets were prepared using a hydrothermal process and used to activate PMS under visible light. A rapid degradation of ciprofloxacin (CIP) was achieved by dosing PMS (0.96 g/L), BiVO₄ (0.32 g/L) under visible light with a reaction rate constant of 77.72-fold higher than that in the BiVO₄/visible light process. The electron spin resonance and free radical quenching experiments indicate that reactive species of ^•O₂^-, h⁺, •OH and SO₄^•- all worked, where h⁺, •OH and SO₄^•- were found as the dominant contributors to the CIP degradation. The spectroscopic analyses further demonstrate that the photoinduced electrons were directly involved in the PMS activation process. The generated ^•O₂^- was partially utilized to activate PMS and more •OH was produced because of the chain reactions between SO₄^•- and H₂O/OH^-. In this process, PMS acted as an electron acceptor to transfer the photo-induced charges from the conduction band of BiVO₄ and PMS was successfully activated to yield the high-powered oxidative species. From the degradation intermediates of CIP detected by a liquid-chromatography-mass spectrometer, the possible degradation pathways were proposed. The substantially decreased toxicity of CIP after the reaction was also observed. This work might provide new insights into the visible-light-assisted PMS activation mechanisms and is useful to construct environmentally-friendly catalytic processes for the efficient degradation of organic pollutants.

TiO2-based catalysts for photocatalytic reduction of aqueous oxyanions: State-of-the-art and future prospects

Nowadays, an increasing discharge of oxyanions to the natural environment has been attracting worldwide attention. TiO₂-based photocatalysis is regarded as one of the most promising technologies for the conversion of toxic oxyanions (such as chromate, nitrate, nitrite, bromate, perchlorate and selenate) to harmless and/or less toxic substances in contaminated waters. Various types of TiO₂-based catalysts have been developed, and each of them exhibits its own advantages in catalytic reduction of oxyanions. However, the application of these nanostructured TiO₂ in real water bodies remains a challenge, with limitations associated with sunlight harvesting abilities, production costs, reuse stability and exposure risks. Herein, we aim to present a critical review on reported TiO₂-based photocatalytic reduction of aqueous oxyanions, provide a comprehensive understanding of the possible reaction pathways of formed active species, and evaluate the reduction performance of different types of TiO₂-based catalysts. In addition, the impact of operating parameters (such as solution pH, temperature, dissolved oxygen and coexisting substances) on catalytic reduction performance is discussed. Furthermore, the perspectives of TiO₂-based photocatalytic reduction of oxyanions are also proposed.

A heterogeneous pore decoration strategy on a hydrophobic microporous polymer for high-coverage capture of metabolites

A heterogeneous pore decoration strategy on a hydrophobic microporous polymer resulted in its hydrophobic–hydrophilic hybrid properties and high-coverage capture ability of microbial metabolites.

Bridging the gap between laboratory and application in photocatalytic water purification

Despite a large number of publications in the field, photocatalytic water treatment is still somewhat disconnected from real world application and we highlight recent developments to address this.

Synergistic photocatalytic performance of cobalt tetra(2-hydroxymethyl-1,4-dithiin)porphyrazine loaded on zinc oxide nanoparticles

A new ZnO/CoPz(hmdtn)₄ composite as a highly efficient photocatalyst was successfully prepared by cobalt tetra(2-hydroxymethyl-1,4-dithiin)porphyrazine (CoPz(hmdtn)₄) impregnated onto the surface of ZnO nanoparticles, the photocatalytic performance of ZnO/CoPz(hmdtn)₄ under both simulated sunlight and visible light (λ ≥ 400 nm) irradiation was assessed by degradation of Rhodamine B (RhB) and phenol in aerated conditions. The ZnO/CoPz(hmdtn)₄ manifested much higher photocatalytic activity than pure ZnO and pure CoPz(hmdtn)₄, originating from the synergistic effect between CoPz(hmdtn)₄ and ZnO. Furthermore, the XPS analysis revealed that there may be strong interaction between CoPz(hmdtn)₄ and ZnO. Thereby ZnO/CoPz(hmdtn)₄ with excellent stability can maintain high photocatalytic activity over five runs on the basis of the reusability test. The active species generated in the photocatalytic system were verified by electron spin resonance (ESR) technology. A possible mechanism of the synergistic effect between CoPz(hmdtn)₄ and ZnO was also proposed.

Biocompatible FeOOH-Carbon quantum dots nanocomposites for gaseous NOx removal under visible light: Improved charge separation and High selectivity

Development of biocompatible photocatalysts with improved charge separation and high selectivity is essential for effective removal of air pollutants. Iron-containing catalysts have attracted extensive attention due to their low-toxicity and high natural abundance. Here, carbon quantum dots (CQDs) modified FeOOH nanocomposites fabricated using a facile hydrothermal route showed enhanced NO removal efficiency (22%) compared to pure FeOOH. Moreover, generation of toxic NO₂ intermediates was significantly inhibited using the nanocomposites, demonstrating high selectivity for final nitrate formation. Photo-electrochemical results showed that both charge separation and transfer efficiency were significantly improved by CQDs addition, and the lifetime of photo-generated carriers was increased eventually. Density functional theory calculations further elucidated that the suppressed recombination of photo-induced electron-hole pairs was due to enhanced electron migration from the FeOOH to CQDs. A NO degradation mechanism was proposed based on detection of the reactive oxygen species using electron paramagnetic spectroscopy. In addition, the nanocomposite showed good biocompatibility and low cytotoxity, ensuring minimal environmental impact for potential application in large-scale.

Photocatalytic degradation properties of α-Fe2O3 nanoparticles for dibutyl phthalate in aqueous solution system

The phthalate ester compounds in industrial wastewater, as kinds of environmental toxic organic pollutants, may interfere with the body's endocrine system, resulting in great harm to humans. In this work, the photocatalytic degradation properties of dibutyl phthalate (DBP) were investigated using α-Fe₂O₃ nanoparticles and H₂O₂ in aqueous solution system. The optimal parameters and mechanism of degradation were discussed by changing the morphology and usage amount of catalysts, the dosage of H₂O₂, pH value and the initial concentration of DBP. Hollow α-Fe₂O₃ nanoparticles showed the highest degradation efficiency when 30 mg of catalyst and 50 µl of H₂O₂ were used in the DBP solution with the initial concentration of 13 mg l^-1 at pH = 6.5. When the reaction time was 90 min, DBP was degraded 93% for the above optimal parameters. The photocatalytic degradation mechanism of DBP was studied by the gas chromatography-mass spectrometry technique. The result showed that the main degradation intermediates of DBP were ortho-phthalate monobutyl ester, methyl benzoic acid, benzoic acid, benzaldehyde, and heptyl aldehyde when the reaction time was 2 h. DBP and its intermediates were almost completely degraded to CO₂ and H₂O in 12 h in the α-Fe₂O₃/ H₂O₂/UV system.

Facile fabrication of direct solid-state Z-scheme g-C3N4/Fe2O3 heterojunction: a cost-effective photocatalyst with high efficiency for the degradation of aqueous organic pollutants

In situ synthesis of a cost-effective g-C₃N₄/Fe₂O₃ hybrid with enhanced photocatalytic activity for the degradation of organic pollutants based on the direct Z-scheme mechanism.