Recent developments in visible-light photocatalytic degradation of antibiotics

With the significant discharge of antibiotic wastewater into the aquatic and terrestrial ecosystems, antibiotic pollution has become a serious problem and presents a hazardous risk to the environment. To address such issues, various investigations on the removal of antibiotics have been undertaken. Photocatalysis has received tremendous attention owing to its great potential in removing antibiotics from aqueous solutions via a green, economic, and effective process. However, such a technology employing traditional photocatalysts suffers from major drawbacks such as light absorption being restricted to the UV spectrum only and fast charge recombination. To overcome these issues, considerable effort has been directed towards the development of advanced visible light-driven photocatalysts. This mini review summarises recent research progress in the state-of-the-art design and fabrication of photocatalysts with visible-light response for photocatalytic degradation of antibiotic wastewater. Such design strategies involve the doping of metal and non-metal into ultraviolet light-driven photocatalysts, development of new semiconductor photocatalysts, construction of heterojunction photocatalysts, and fabrication of surface plasmon resonance-enhanced photocatalytic systems. Additionally, some perspectives on the challenges and future developments in the area of photocatalytic degradation of antibiotics are provided.

Achieving high-efficient photocatalytic persulfate-activated degradation of tetracycline via carbon dots modified MIL-101(Fe)octahedrons

The synergistic reaction of photocatalysis and advanced oxidation is a valid strategy for the degradation of harmful antibiotic wastewater.Herein,carbon dots(CDs)modified MIL-101(Fe)octahedrons to form CDs/MIL-101(Fe)composite photocatalyst was synthesized for visible light-driven photocatalytic/persulfate(PS)-activated tetracycline(TC)degradation.The electron spin resonance(ESR)spectra,scavenging experiment and electrochemical analysis were carried out to reveal that the high visible light-driven photocatalytic degradation activity of TC over CDs/MIL-101(Fe)photocatalysts is not only ascribed to the production of free active radicals in the CDs/MIL-101(Fe)/PS system(·OH,·SO_(4-),^(1)O_(2),h^(+)and·O_(2)^(-))but also attributed to the consumption of electrons caused by the PS,which can suppress the recombination of photo-generated carriers as well as strong light scattering and electron trapping effects of CDs.Finally,the possible degradation pathways were proposed by analyzing intermediates via liquid chromatography-mass spectrometry technique.This research presents a rational design conception to construct a CDs/PS-based photocatalysis/advanced oxidation technology with high-efficient degradation activity for the remediation of organic antibiotic pollutant wastewater and for the improvement of carrier transport kinetics of photocatalysts.

Photocatalytic degradation of methylene blue over MIL-100(Fe)/GO composites: a performance and kinetic study

Adsorption coupled with photocatalytic degradation is proposed to fulfill the removal and thorough elimination of organic dyes.Herein,we report a facile hydrothermal synthesis of MIL-100(Fe)/GO photocatalysts.The adsorption and photocatalytic degradation process of methylene blue(MB)on MIL‐100(Fe)/GO composites were systematically studied from performance and kinetic perspectives.A possible adsorption‐photocatalytic degradation mechanism is proposed.The optimized 1M8G composite achieves 95%MB removal(60.8 mg/g)in 210 min and displays well recyclability over ten cycles.The obtained MB adsorption and degradation results are well fitted onto Langmuir isotherm and pseudo‐second order kinetic model.This study shed light on the design of MOFs based composites for water treatment.

Photocatalytic Degradation of Plastic Waste: Recent Progress and Future Perspectives

Microplastics are persistent anthropogenic pollutants that have become a global concern due to their widespread distribution and unfamiliar threat to the environment and living organisms. Conventional technologies are unable to fully decompose and mineralize plastic waste. Therefore, there is a need to develop an environmentally friendly, innovative and sustainable photocatalytic process that can destroy these wastes with much less energy and chemical consumption. In photocatalysis, various nanomaterials based on wide energy band gap semiconductors such as TiO2 and ZnO are used for the conversion of plastic contaminants into environmentally friendly compounds. In this work, the removal of plastic fragments by photocatalytic reactions using newly developed photocatalytic composites and the mechanism of photocatalytic degradation of microplastics are systematically investigated. In these degradation processes, sunlight or an artificial light source is used to activate the photocatalyst in the presence of oxygen.

Pomelo biochar as an electron acceptor to modify graphitic carbon nitride for boosting visible-light-driven photocatalytic degradation of tetracycline

In this study,biochar(BC)derived from pomelo was prepared via a high-temperature calcination method to modify the graphitic carbon nitride(g-C_(3)N_(4))to synthesize the BC/g-C_(3)N_(4)composite for the degradation of the tetracycline(TC)antibiotic under visible light irradiation.The experimental results exhibit that the optimal feeding weight ratio of biochar/urea is 0.03:1 in BC/g-C_(3)N_(4)composite could show the best photocatalytic activity with the degradation rate of tetracycline is 83%in 100 min irradiation.The improvement of photocatalytic activity is mainly attributed to the following two points:(i)the strong bonding with π-π stacking between BC and g-C_(3)N_(4)make the photogenerated electrons of light-excited g-C_(3)N_(4)transfer to BC,quickly and improve the separation efficiency of carriers;(ii)the introduction of BC reduces the distance for photogenerated electrons to migrate to the surface and increases the specific surface area for providing more active sites.This study provides a sustainable,economical and promising method for the synthesis of photocatalytic materials their application to wastewater treatment.

Highly efficient visible-light photocatalytic degradation and antibacterial activity by GaN:ZnO solid solution nanoparticles

The development of high-efficiency photocatalysts is the primary goal in the field of photocatalytic antibacterial research.In this work,the Ga N:Zn O solid solution nanoparticles(NPs)photocatalyst with strong visible absorption and large specific surface area was synthesized via the sol-gel and nitridation reaction process.Also,we systematically investigated the removal efficiency of the organic pollutant and antibacterial activity on E.coli and S.aureus.Notably,methylene blue solution could be completely degraded after 100 min of visible light illumination using 2 mg/m L Ga N:Zn O catalyst.Moreover,~94%of the E.coli were inactivated within 120 min,whereas 100%antibacterial activity against S.aureus was achieved after 90 min of visible light illumination mediated by Ga N:Zn O NPs.We further explore the potential mechanism of visible light photocatalytic antibacterial activity enhanced by Ga N:Zn O NPs photocatalyst.The current work not only provides a new and efficient photocatalytic antibacterial nanomaterial but also demonstrates its promising applications in environmental and biological fields.

ZnFe_(2)O_(4)/BiVO_(4)Z-scheme heterojunction for efficient visible-light photocatalytic degradation of ciprofloxacin

A novel Z-scheme ZnFe_(2)O_(4)/BiVO_(4)heterojunction photocatalyst was successfully synthesized using a convenient solvothermal method and applied in the visible light photocatalytic degradation of ciprofloxacin,which is a typical antibiotic contaminant in wastewater.The heterostructure of as-synthesized catalysts was confirmed using X-ray diffraction,scanning electron microscopy,transmission electron microscopy and X-ray photoelectron spectroscopy characterizations.Compared with the singlephase counterparts,ZnFe_(2)O_(4)/BiVO_(4)demonstrated considerably enhanced photogenerated charge separation efficiencies because of the Z-scheme transfer mechanism of electrons between the composite photocatalysts.Consequently,the 30%ZnFe_(2)O_(4)/BiVO_(4)catalyst afforded a degradation rate of up to 97%of 20 mg/L ciprofloxacin under 30 min of visible light irradiation with a total organic carbon removal rate of 50%,which is an excellent activity compared with ever reported BiVO_(4)-based catalysts.In addition,the liquid chromatography-mass spectrometry and quantitative structure-activity relationships model analyses demonstrated that the toxicity of the intermediates was lower than that of the parent ciprofloxacin.Moreover,the as-synthesized ZnFe_(2)O_(4)/BiVO_(4)heterojunctions were quite stable and could be reused at least four times.This study thus provides a promising Z-scheme heterojunction photocatalyst for the efficient removal and detoxication of antibiotic pollutants from wastewater.

Enhanced photocatalytic degradation of sulfadiazine by Fe^(3+) in aqueous TiO_2 suspension

In order to explore the reaction mechanism of Fe^3＋ and the mineralization effect of the micropollutant, Fe^3＋ assisted photocatalytic oxidation of sulfadiazine （SD） in the TiO2 suspended solution is investigated. The effect of Fe^3＋ participation, the degradation kinetics of SD, the effect of SD mineralization and the possible mechanism of Fe^3＋ participation in TiO2 suspension are analyzed by adding FeCl3, taking samples at a given time and determining the SD concentration. Results indicate that the degradation of SD catalyzed by TiO2/ Fe^3＋ is faster than that catalyzed by TiO2 or Fe^3＋ separately. The photocatalytic degradation of SD follows the pseudo-first- order kinetics model in a range of 20 to 80 mg/L of initial concentration. The mineralization rate of SD can be enhanced by the addition of Fe^3＋ in the TiO2 suspended solution. The mechanism of the rapid degradation of SD is proposed, which indicates that Fe^3＋ adsorbed on the surface of TiO2 particles acts as an electron acceptor. The amount of recombining electronhole pairs decreases, and the amount of hydroxyl radicals increases. The increased hydroxyl radical strengthens the degradation of SD in the TiO2/Fe^3＋ suspended solution.

Plasmonic Ag nanoparticles decorated g-C_(3)N_(4)for enhanced visible-light driven photocatalytic degradation and H_(2)production

The plasmonic Ag nanoparticles(NPs)loaded g-C_(3)N_(4)photocatalysts(Ag/C_(3)N_(4))were successfully prepared via a conventional procedure.The fully characterized Ag/C_(3)N_(4)photocatalysts exhibited excellent stability and greatly enhanced visible light-driven photocatalytic performance both in the degradation of methyl orange(MO)and H_(2)evolution from water splitting.The 1.0 wt%Ag/C_(3)N_(4)allowed the highest reaction rate of 0.0294 min^(−1)to be obtained in the MO degradation,which is about 2.3 times higher than the reaction rate of g-C_(3)N_(4)alone of 0.0129 min^(−1).Furthermore,the optimum H_(2)evolution and the k value attained 20μmol and 1.573 h^(−1),respectively,after 12 h of visible light irradiation.The surface plasmon resonance effect of Ag NPs and the charge transfer between the two components of the photocatalyst,strongly promote generation of photoinduced charge carriers while suppressing their recombination.These factors are held responsible for the enhanced visible light photocatalytic performance of Ag/C_(3)N_(4).Our methodology will provide guidance for the design and synthesis of plasmon-enhanced visible light photocatalysts derived from Ag NPs and g-C_(3)N_(4)and their applications in environmental remediation and green energy development.

Photocatalytic Degradation of Water-Soluble Dyes by LaCoO_3

Pervoskite type oxides LaCoO 3 was prepared by citrate method with the granula of 20 nm-30 nm. With a fluorescent Hg lamp or sunlight as irradiator, the degradation experiments of various water soluble dyes were carried out in the suspension system of LaCoO 3 . The results show that the pervoskite type oxide LaCoO 3 has good photocatalytic activity.Studied by X ray photoelectron spectroscopy and photoacoustic spectra, its photocatalytic activity is found to be related with factors such as the d electron structure of ion Co 3+ ,Co—O binding energy and adsorbed oxygen on the surface etc.

Photocatalytic Degradation of Phenol over MWCNTs-TiO2 Composite Catalysts with Different Diameters

Titania-based composite catalysts were prepared through a sol-gel route employing multi-walled carbon nanotubes with different diameters. The materials were characterized using thermogravimetric analysis, nitrogen adsorption-desorption isotherm, powder X-ray diffraction, scanning electron microscopy, and diffuse reflectance UV-Vis absorption spectra. The application of the catalysts to photocatalytic degradation of phenol was tested under UV-Vis irradiation. A synergetic effect on phenol removal was observed in case of composite catalysts, which was evaluated in terms of apparent rate constant, total organic carbon removal and photonic efficiency.

Photocatalytic Degradation of Water-Soluble Dyes by LaCoO3

Pervoskite type oxides LaCoO 3 was prepared by citrate method with the granula of 20 nm-30 nm. With a fluorescent Hg lamp or sunlight as irradiator, the degradation experiments of various water soluble dyes were carried out in the suspension system of LaCoO 3 . The results show that the pervoskite type oxide LaCoO 3 has good photocatalytic activity.Studied by X ray photoelectron spectroscopy and photoacoustic spectra, its photocatalytic activity is found to be related with factors such as the d electron structure of ion Co 3+ ,Co—O binding energy and adsorbed oxygen on the surface etc.

Microwave photocatalytic degradation of Rhodamine B using TiO_2 supported on activated carbon:Mechanism implication

The photocatalytic degradation of Rhodamine B （RhB） was carried out using TiO2 supported on activated carbon （TiO2-AC） under microwave irradiation. Composite catalyst TiO2-AC was prepared and characterized using X-ray diffraction （XRD）, transmission electron microscopy （TEM） and Brunauer-Emmett-Teller （BET）. In the process of microwave-enhanced photocatalysis （MPC）, RhB （30 mg/L） was almost completely decoloured in 10 min, and the mineralization efficiency was 96.0% in 20 min. The reaction rate constant of RhB in MPC using TiO2-AC by pseudo first-order reaction kinetics was 4.16 times of that using Degussa P25. Additionally, according to gas chromatography/mass spectrometry （GC/MS） and liquid chromatography/mass spectrometry （LC/MS） identification, the major intermediates of RhB in MPC included two kinds of N-de-ethylation intermediates （N,N-diethyl-N＇-ethyl-rhodamine （DER））, oxalic acid, malonic acid, snccinic acid, and phthalic acid, maleic acid, 3-nitrobenzoic acid, and so on. The degradation of RhB in MPC was mainly attributed to the destruction of the conjugated structure, and then the intermediates transformed to acid molecules which were mineralized to water and carbon dioxide.

Photocatalytic degradation of the dye sulforhodamine-B: A comparative study of different light sources

The photocatalytic degradation of dye pollutant sulforhodamine-B （SRB） in aqueous titanium dioxide （TiO2） dispersions was examined under three lighting regimes： UV light （330 nm〈λ〈 380 nm）, sunlight, and visible light （λ〉450 nm）, all investigated at pH=2.5. Total organic carbon （TOC） and chemical oxygen demand （CODer） assays show that the degradation rate of SRB is much higher when irradiated with UV and sunlight compared with visible light. The temporal concentration changes of SRB illustrated a first-order reaction and the rate constant, k, is 0.197 min^-1, 0.152 min^-1, 0.027 min^-1, respectively, under the three lighting conditions. The final mineralized products were amine compounds identified by infrared spectrophotometry. When irradiated with visible light, the photocatalytic degradation rate could be improved by lowering the H2O2 concentration and inhibited by increasing the H2O2 concentration, but results contrary to the above were obtained when UV light was used for irradiation.

Effects of common inorganic anions on the rates of photocatalytic degradation of sodium dodecylbenzenesulfonate over illuminated titanium dioxide

Experiments were carried out to study the effects of several anions on the photocatalytic degradation rates of sodium dodecylbenzene sulphonate (DBS) with TiO 2 as catalyst. The anions were added as Na 2SO 4, NaNO 3, NaCl, NaHCO 3, NaH 2PO 4 and Na 3PO 4, and two levels of anion content, i.e. 12 mmol/L and 36 mmol/L in terms of Na +, were studied. The results revealed that: Cl -, SO 2- 4, NO - 3 and HCO - 3 retarded the rates of DBS degradation to different degrees; PO 3- 4 increased the DBS degradation rate at low concentration and decreased the rate at high concentration; H 2PO - 4 accelerated the rate of DBS degradation. The mechanism of the effects of anions on DBS degradation was concluded as the following three aspects: anions compete for the radicals; anions are absorbed on the surface of catalyst and block the active site of catalyst; anions added to the solution change the pH value and influence the formation of ·OH radicals and the adsorption of DBS on catalyst.

Preparation of nano-TiO_2/diatomite-based porous ceramics and their photocatalytic kinetics for formaldehyde degradation

Diatomite-based porous ceramics were adopted as carriers to immobilize nano-TiO2 via a hydrolysis-deposition technique. The thermal degradation of as-prepared composites was investigated using thermogravimetric-differential thermal analysis, and the phase and microstructure were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and transmission electron microscopy. The results indicated that the carriers were encapsulated by nano-TiO2 with a thickness of 300-450 nm. The main crystalline phase of TiO2 calcined at 650~C was anatase, and the average grain size was 8.3 nm. The FT-IR absorption bands at 955.38 cm1 suggested that new chemical bonds among Ti, O, and Si had formed in the composites. The photocatalytic （PC） activity of the composites was investigated un- der UV irradiation. Furthermore, the photodegradation kinetics of formaldehyde was investigated using the composites as the cores of an air cleaner. A kinetics study showed that the reaction rate constants of the gas-phase PC reaction of formaldehyde were k = 0.576 mg＇m3·min^-1 and K = 0.048 m3/mg.

Photocatalytic Degradation of Water-Soluble Dyes by LaCoO_3

Perovskite type oxides LaCoO 3 was prepared by citrate method in granula of 20～30 nm. Using a fluorescent Hg lamp or sunlight as irradiator, the degradation experiments of various water soluble dyes were carried out in the suspension system of LaCoO 3. The results show that the perovskite type oxide LaCoO 3 has good photocatalytic activity. With the study of X ray photoelectron spectroscopy and photoacoustic spectra, its photocatalytic activity is mainly related with the factors such as the d electron structure of ion Co 3+ , Co O binding energy and adsorbed oxygen on the surface etc.

Photocatalytic degradation of acid orange 7 in aqueous solution with La^(3+)-doped TiO_2 photocatalysts

Nanocrystalline La^3＋-doped TiO2 of 20-30 nm in size was prepared by a sol-gel technique. The photocatalytic activities of the samples were evaluated by the degradation of harmful acid orange 7（AO7） azo-dye in aqueous solution. The effects of La^3＋ ion implantation on the photocatalytic activity of TiO2 were also discussed. The results show that the La^3＋ content plays an essential role in affecting the photocatalytic activity of the La^3＋-doped TiO2 and the optimum content of La^3＋-doped is 1.0 wt.%. The photocatalytic activity of the samples with La^3＋-doped TiO2 is higher than that of pure TiO2 in the treatment of AO7 wastewater. The photodegradation effect of AO7 effluent is the best by means of La^3＋-doped TiO2 with 1.0% La^3＋.

Photocatalytic degradation of MO by complex nanometer particles WO_3/TiO_2

Complex nanometer particles WO3/TiO2 were prepared using a sol-gel process and characterized using XRD spectra. The photocatalytic activity of TiO2 can be increased by doping W^6＋ with TiO2 because the doped W^6＋ that entered into the crystal lattices of TiO2 led to the formation of defects in the crystal lattices of TiO2 and thereby improved the photocatalytic activity of TiO2.When WO3 doped in TiO2 exceeded 3%, the excess W^6＋ did not enter into the crystal lattices of TiO2 but were uniformly dispersed in TiO2 or they covered the surface of TiO2, which reduced the effective illumination area of TiO2 and thereby lowered the photocatalytic activity of TiOE.The relationship among the composition of the catalyst, the amount of photocatalyst, the illumination time, and the decolorizing rate of methyl orange （MO） were discussed. The results show that the decolorizing rate of MO can reach 82.3% using WO3/TiO2 as the photocatalyst, with the composition of WO3/TiO2 -3：97, the mass of catalyst = 0.400 g, the initial concentration of MO = 20 mg/L, pH = 6.5, and the illumina- tion time = 7 h.

Photocatalytic degradation of dyes by AgBr/Ag_3PO_4 and the ecotoxicities of their degraded products

Ag3PO4 powders were prepared through a precipitation reaction between AgNO3 and precipitating agent solutions that were prepared by adjusting the amount of H3PO4 in the Na3PO4 solutions. The Ag3PO4 powders prepared from the precipitation solution with a pH of 6 showed the highest photocatalytic activity for decolorizing the methylene blue and rhodamine B dyes. These Ag3PO4 powders were further modified by the addition of KBr solutions to obtain AgBr/Ag3PO4 powders and these photocatalysts can decolorize the anionic dyes as reactive orange and methyl orange. The reactive species involved in the photocatalytic degradation process were evaluated for their inhibitory activity using the appropriate scavengers. After photocatalysis, mass spectrometry confirmed that the dyes were degraded to smaller molecules. The ecotoxicities of the dye solutions before and after treatment were evaluated by studying their ability to inhibit the growth of the bioindicator Chlorella vulgaris.