Fe2.5Co0.3Zn0.2O4/CuCr-LDH as a visible-light-responsive photocatalyst for the degradation of caffeine, bisphenol A, and simazine in pure water and real wastewater under photo-Fenton-like degradation process

Catalytic degradation of crystal violet and methyl orange in heterogeneous Fenton-like processes

Metals-loaded (Fe3+, Cu2+ and Zn2+) activated carbons (M@AC) with different loading ratios (0.1%, 0.5%, 1%, 5% and 10%) were prepared and employed for catalytic degradation of dye model compounds (crystal violet (CV) and methyl orange (MO)) in wastewater by heterogeneous Fenton-like technique. Compared with Cu@AC and Zn@AC, 0.5% Fe3+ loaded AC (0.5Fe@AC) had better catalytic activity for dyes degradation. The effects of dyes initial concentration, catalyst dosage, pH and hydrogen peroxide (H2O2) volume on the catalytic degradation process were investigated. Cyclic performance, stability of 0.5Fe@AC and iron leaching were explored. Degradation kinetics were well fitted to the pseudo-second-order model (Langmuir-Hinshelwood). Almost complete decolorization (99.7%) of 400 mg L-1 CV was achieved after 30 min reaction under the conditions of CV volume (30 mL), catalyst dosage (0.05 g), H2O2 volume (1 mL) and pH (7.7). Decolorization of MO reached 98.2% under the same conditions. The abilities of pyrolysis char (PC) of dyeing sludge (DS) and metal loaded carbon to remove dye pollutants were compared. The intermediate products were analyzed and the possible degradation pathway was proposed. This study provided an insight into catalytic degradation of triphenylmethane- and aromatic azo-based substances, and utilization of sludge char.

Study on the behavior and mechanism of NiFe-LDHs used for the degradation of tetracycline in the photo-Fenton process

An environment-friendly 3D NiFe-LDHs photocatalyst was fabricated via a simple hydrothermal method and characterized by means of SEM, XRD, BET, XPS and FT-IR. It is a highly efficient heterogeneous photo-Fenton catalyst for the degradation of TC-HCl under visible light irradiation. After exploring the effects of catalyst dosage, initial concentration of TC-HCl, solution pH and H2O2 concentrations, the optimal reaction conditions were determined. The experiment results showed that the degradation efficiency can reach 99.11% through adding H2O2 to constitute a photo-Fenton system after adsorption for 30 min and visible light for 60 min. After four cycles, the degradation rate decay is controlled within 21.2%, indicating that NiFe-LDHs have excellent reusable performance. The experimental results of environmental factors indicate that Fe2+ and Ca2+ promoted the degradation of TC-HCl, both Cl- and CO32- inhibited the degradation of TC-HCl. Two other antibiotics (OTC and FT) were selected for research and found to be effectively removed in this system, achieving effective degradation of a variety of typical new pollutants. The radical trapping tests and ESR detection showed that ·OH and ·O2- were the main active substances for TC degradation in the photo-Fenton system. By further measuring the intermediate products of photodegradation, the degradation pathway of TC-HCl was inferred. The toxicity analysis demonstrated that the overall toxicity of the identified intermediates was reduced in this system. This study provides a theoretical and practical basis for the removal of TC in aquatic environments.

Mechanochemical Degradation of Caffeine and Diclofenac Using Biochar of Fique Bagasse in the Presence of Al: Monitoring by Mass Spectrometry

Much research has been carried out to remove emerging contaminants using diverse materials. Furthermore, studies related to pollutant degradation have increased over the past decade. Mechanochemical degradation can successfully decompose molecules that are persistent in the environment. In this study, the biochar of fique bagasse with mixtures SiO2, Al, Al2O3, and Al-Al2O3 was treated with a mechanochemical technique using a planetary ball mill to investigate the degradation of caffeine and diclofenac. These tests resulted in the transformation of caffeine and diclofenac due to the use of Al employing mechanochemistry. In fact, through the use of liquid chromatography coupled with mass spectrometry, eight and six subproducts were identified for caffeine and diclofenac, respectively. Additionally, analysis of the molecules proposed for caffeine and diclofenac transformation suggested hydroxylation, demethylation, decarboxylation, oxidation reactions, and cleavage of the C-C and C-N bonds in the pollutants studied. The formation of these transformation products could be possible by reductant oxygen species generated from the molecular oxygen in the presence of aluminum and the energy delivered for ball milling. The results obtained show the potential application in the environmental management of mechanochemical treatment in the elimination of emerging contaminants caffeine and diclofenac.

Insight into Chinese medicine residue biochar combined with ultrasound for persulfate activation in atrazine degradation: Acanthopanax senticosus precursors, synergistic effects and toxicity assessment

The synergistic activation of persulfate by multiple factors could degrade pollutants more efficiently. However, the co-activation method based on metal ions has the risk of leakage. The non-metallic coupling method could achieve the same efficiency as the metal activation and meanwhile release environmental stress. In this study, the original biochar (BC) was prepared through using Chinese medicinal residue of Acanthopanax senticosus as the precursor. Compared with other biochar, the pore size structure was higher and toxicity risk was lower. The ultrasonic (US)/Acanthopanax senticosus biochar (ASBC)/persulfate oxidation system was established for Atrazine (ATZ). Results showed that 45KHz in middle and low frequency band cooperated with ASBC600 to degrade nearly 70 % of ATZ within 50 min, and US promoted the formation of SO₄^- and OH. Meanwhile, the synergy index of US and ASBC was calculated to be 1.18, which showed positive synergistic effect. Finally, the potential toxicity was examined by using Toxicity Characteristic Leaching Procedure (TCLP) and luminescent bacteria. This study provides a promising way for the activation of persulfate, which is expected to bring a new idea for the win-win situation of pollutant degradation and solid waste resource utilization.

Mechanisms of biochar enhanced Cu2O photocatalysts in the visible-light photodegradation of sulfamethoxazole

Cu₂O nanoparticles are decorated with biochars derived from spent coffee grounds (denoted as Cu₂O/SCG) and applied as visible-light-active photocatalysts in the sulfamethoxazole (SMX) degradation. The physicochemical properties of Cu₂O/SCG are identified by various spectral analysis, electrochemical and photochemical techniques. As a result, the Cu₂O/SCG exhibits the higher removal efficiency of SMX than the pristine Cu₂O under visible light irradiation. We can observe that Cu₂O could be incorporated onto the SCG biochars with rich oxygen vacancies/adsorbed hydroxyl groups. In addition, the Cu₂O/SCG has the lower charge transfer resistance, faster interfacial electron transfer kinetics, decreased recombination of charge carriers and superior absorbance of visible light. The construction of band diagrams for Cu₂O/SCG and pristine Cu₂O via UV-vis spectra and Mott-Schottky plots suggest that the band energy shifts and higher carrier density of Cu₂O/SCG may be responsible for the photocatalytic activity enhancements. From the radical scavenger experiments and electron paramagnetic resonance spectra, the aforementioned energy shifts could decrease the energy requirement of transferring photoinduced electrons to the potential for the formation of active superoxide radicals (·O₂^-) via one and two-electron reduction routes in the photocatalytic reaction. A proposed degradation pathway shows that ·O₂^- and h⁺ are two main active species which can efficiently degrade SMX into reaction intermediates by oxidation, hydroxylation, and ring opening. This research demonstrates the alternative replacement of conventional carbon materials for the preparation of biochar-assisted Cu₂O photocatalysts which are applied in the environmental decontamination by using solar energy.

Zinc-chromium layered double hydroxides anchored on carbon nanotube and biochar for ultrasound-assisted photocatalysis of rifampicin

In this study, ZnCr layered double hydroxide (LDH), ZnCr LDH/carbon nanotube (CNT), and ZnCr LDH/Biochar (BC) were synthesized and characterized by various analyses. The successful synthesis and the great crystallinity of the samples were consented by XRD analysis. SEM and TEM were applied to study the morphology of the synthesized samples. The simultaneous presence of C, Zn, and Cr elements was well confirmed by EDX and dot mapping analyses demonstrating the successful preparation of nanocomposites. According to the BET analysis, ZnCr LDH nanocomposites with BC and CNT had more specific surface area compared to ZnCr LDH alone. The catalytic performances of the samples were determined for the degradation of rifampicin (RF). The degradation efficiency of the sonophotocatalytic process in the presence of 0.6 g L^-1 of ZnCr LDH/BC toward 15 mg L^-1 of RF under 150 W ultrasound and visible light irradiation was found to be about 100% within 40 min. The influence of the reactive species on the sonophotocatalytic process was assessed via the addition of different scavengers (para-benzoquinone (p-BQ), formic acid (FA), isopropyl alcohol (IPA)), and enhancers (hydrogen peroxide and potassium persulfate). The GC-MS analysis was carried out and eleven by-products during the RF decomposition were detected.