Synthesis of ZnO immobilized on recycled polyethylene terephtalate for sonocatalytic removal of Cr(VI) from synthetic, drinking waters and electroplating wastewater

Photocatalytic degradation of reactive black 5 from synthetic and real wastewater under visible light with TiO2 coated PET photocatalysts

The photocatalytic removal of Reactive Black 5 (RB5) was investigated using a titanium dioxide-polyethylene terephthalate (TiO2-PET) catalyst under visible (VIS) light. The sol-gel method was employed for the fabrication of the TiO2-coated PET catalyst, which was then characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and elemental mapping (MAP) analysis. This study examined the reaction kinetics using the one-factor-at-a-time (OFAT) approach and evaluates the effects of various parameters, including pH (3-11), catalyst dosage (0.1-1 g L- 1), contact time (15-120 min), RB5 concentration (10-50 mg L- 1), hydrogen peroxide (H2O2) content (2-100 mM), purging gases, organic compound types, and ionic strength, on the photocatalytic removal of RB5. Under optimal conditions (pH= 3, [RB5]°= 20 mg L- 1, nanocatalyst dosage= 0.5 g L- 1), 99.99% of the dye was removed after 120 min. Increasing the RB5 concentration (10-50 mg L- 1) resulted in a decrease in the observed reaction rate constant (kobs) from 0.052 to 0.0017 min- 1, while the calculated electrical energy per order (EEO) increased from 11.08 to 338.82 kWh m- 3. Furthermore, the total operating cost of the light emitting diode (LED)/TiO2-PET process (3 USD kg- 1) was lower than that of other photocatalytic processes, including LED/TiO2 (4.73 USD kg- 1), LED/PET (40 USD kg- 1), and LED (63.16 USD kg- 1). The removal of RB5 was negatively affected by the presence of H2O2, O2 and N2 gases, organic compounds, and ionic species. Radical quenching experiments confirmed that hydroxyl radicals (·OH) were the dominant reactive species responsible for RB5 degradation. The RB5 removal efficiency using the LED/TiO2-PET method (99.99%) was significantly higher than that of the LED/TiO2 method (63.42%). Desorption experiments demonstrated excellent catalyst stability, maintaining catalytic activity for up to five sequential cycles. GC-MS analysis identified several intermediate degradation products, including 1,2-benzenedicarboxylic acid, benzoic acid (2-amino-, methyl ester), benzene [(methylsulfonyl) methyl], phenol, 4-naphthalenedione, acetic acid, and propionic acid. Moreover, the removal efficiency in drinking water samples was approximately 63.31%, whereas for real textile wastewater samples, it reached 96.66%. Toxicity tests conducted on the final treated solutions confirmed no toxicity toward Daphnia magna, demonstrating the effectiveness of the LED/TiO2-PET method in degrading both RB5 dye and its toxic by-products.

Sustainable pollution removal and resources recovery from electroplating wastewater by coagulation, advanced oxidation coupling with bioaugmentation

Electroplating wastewater contains high concentrations of dissolved organic matter, heavy metal ions (HMs), refractory organic compounds (ROC), and the complicated composition of effluents. Bioaugmentation presents an efficient strategy for eliminating pollution and recycling resources from electroplating effluent. In this study, simultaneous removal of pollution and sustainable resources recovery from electroplating wastewater were conducted by polyferric sulfate (PFS)-based coagulation, ultraviolet (UV)-activated persulfate (PS) (UV-APS)-based advanced oxidation coupling with bioaugmentation. To reduce carbon emissions and achieve carbon neutrality, genetically engineered Vibrio natriegens with an aerobic sulfate reduction pathway (GeVin) was introduced to remove sulfate, organics, and HMs, which further promoted generation of metal sulfides. The results of coagulation by PFS eliminated 34.68% of chemical oxygen demand (COD), 38.56% of ammonia nitrogen (NH4-N), 36.30% of ROC, and 16.67% of HMs. The rest of refractory contaminants in the effluent of coagulation were oxidatively degraded by UV-APS to improve biodegradability index. The bioaugmentation using immobilized GeVin (IMGevin) coupled with membrane bioreactor (MBR) (IMGevin-MBR) significantly removed 98.25% of COD, 96.23% of NH4-N, 99.42% of biochemical oxygen demand (BOD), 97.85% of sulfate, and 97.68% of HMs. Mechanism analysis indicated that sulfate derived from PFS-based coagulation and UV-APS provided more electron acceptors to generate H2S metabolized by GeVin, contributing to HMs removal via sulfate reduction pathway. Furthermore, IMGeVin-MBR decreased startup phase, hydraulic retention time (HRT), increased the microbial activity, functional microbial community and abundances of genes related to sulfate metabolism, resulting in improvement of systemic stability. Meanwhile, IMGeVin-MBR decreased the total treatment cost, sludge yields, and greenhouse gas (GHG) emissions for treatment of electroplating wastewater. In conclusion, this study provides a sustainable pollution removal and resources recovery strategy for treating electroplating wastewater.

Catalytic wet air oxidation removal of tetracycline by La2O3 immobilized on recycled polyethylene terephthalate using the response surface methodology

This study investigated the removal of tetracycline from the aqueous solutions by lanthanum oxide nanoparticles covered with polyethylene terephthalate (PET) using a low-cost and facile co-precipitation method, via catalytic wet air oxidation process (CWAO) by response surface methodology (RSM). XRD, FTIR, SEM, and EDX-map techniques have been employed to investigate the crystal structure, functional groups on the surface, morphologic characteristics, and elemental composition, respectively. Under optimum conditions (pH= 9, initial TC concentration= 20 mg L-1, nanocomposite dosage= 1.5 g L-1, pressure= 4 bar, temperature= 70 °C, and time= 90 min), TC removal efficiency by La2O3-PET was achieved at about 99.9%. The environmental parameters were assessed to determine tetracycline catalytic wet air oxidation degradation rate, which included cleaning gases, hydrogen peroxide, type of organic compounds, anions, radical scavenger and reusability. The ANOVA results indicated that the polynomial model proves that the model is entirely meaningful (F-value> 0.001 and P-value< 0.0001) and has high coefficient values of adjusted R2 (0.7404) and predicted R2 (0.5940). The findings indicated that the variables of time, pH, temperature, dosage, and TC concentration have the greatest role in removing tetracycline, respectively. However, pressure as a factor does not have a considerable influence on the performance of the system. In general, due to the presence of the role of additional anionics, the effectiveness of this method for removing tetracycline from drinking water was 82.76%. The catalyst indicated pleasing stability and recycling power during eight testing cycles. Further, the estimated electrical energy per order consumption (EEO) for the CWAO/La2O3-PET system was calculated as 5.31 kWh m-3 with an operational cost (OC) utilization of 1.78 USD kg-1 and it has been shown that this process is feasible and economically comparable to other CWAO processes. The breakdown intermediate products of tetracycline in the CWAO were examined using gas chromatography/mass spectrometry (GC-MS) analysis. The toxicity analyses for the removal of TC were carried out using Daphnia magna and the CWAO process achieved a remarkable decrease in the presence of La2O3-PET nanocomposite (LC50 and toxicity unit (TU) 48 h equal to 0.634 and 157.72 vol percent).

A waste-to-wealth conversion of plastic bottles into effective carbon-based adsorbents for removal of tetracycline antibiotic from water

Currently, plastic waste and antibiotic wastewater are two of the most critical environmental problems, calling for urgent measures to take. A waste-to-wealth strategy for the conversion of polyethylene terephthalate (PET) plastic bottles into value-added materials such as carbon composite is highly recommended to clean wastewater contaminated by antibiotics. Inspired by this idea, we develop a novel PET-AC-ZFO composite by incorporating PET plastic-derived KOH-activated carbon (AC) with ZnFe2O4 (ZFO) particles for adsorptive removal of tetracycline (TTC). PET-derived carbon (PET-C), KOH-activated PET-derived carbon (PET-AC), and PET-AC-ZFO were characterized using physicochemical analyses. Central composite design (CCD) was used to obtain a quadratic model by TTC concentration (K), adsorbent dosage (L), and pH (M). PET-AC-ZFO possessed micropores (d ≈ 2 nm) and exceptionally high surface area of 1110 m2 g-1. Nearly 90% TTC could be removed by PET-AC-ZFO composite. Bangham kinetic and Langmuir isotherm were two most fitted models. Theoretical maximum TTC adsorption capacity was 45.1 mg g-1. This study suggested the role of hydrogen bonds, pore-filling interactions, and π-π interactions as the main interactions of the adsorption process. Thus, a strategy for conversion of PET bottles into PET-AC-ZFO can contribute to both plastic recycling and antibiotic wastewater mitigation.

Plant-mediated synthesis of silver-doped ZnO nanoparticles with high sonocatalytic activity: Sonocatalytic behavior, kinetic and thermodynamic study

Together with the rapid growth of technology, the discharge of wastewater from industry into environment had become a hot topic among society nowadays. More attention had been given to the development of water treatment techniques. In this study, sonocatalysis was proposed to degrade the organic pollutants using silver-doped zinc oxide (Ag-ZnO) nanoparticles which were synthesized via green synthesis process using Clitoria ternatea Linn (Asian Pigeonwings flower). The characterization results revealed that the incorporation of Ag into the ZnO lattice decreased the crystallite size and increased the specific surface area of ZnO nanoparticles. It is noteworthy that about 98% of sonocatalytic degradation efficiency of malachite green (MG) was successfully achieved within 30 min in the presence of 5 wt.% Ag-ZnO with 1.0 g/L of catalyst loading under 500 mg/L of initial dye concentration, 80 W of ultrasonic power, 45 kHz of ultrasound frequency, and 2.0 mM of oxidant concentration. The kinetic study showed that the sonocatalytic degradation of organic dye was fitted well into second-order kinetic model with high R2 value (0.9531). In the thermodynamic study, negative value of standard Gibbs free energy and low value of activation energy (+ 24.43 kJ/mol) were obtained in the sonocatalytic degradation of MG using the green-synthesized Ag-ZnO sample. HIGHLIGHTS: • Facile synthesis of silver-doped zinc oxide nanoparticles using plant extract which act as reducing and stabilizing agents • Optical, physical, and chemical characterization of green-synthesized nanomaterials were performed • Evaluation of sonocatalytic degradation of organic dye using green-synthesized nanomaterials • Sonocatalytic behavior, kinetic and thermodynamic studies of sonocatalytic reaction.

Preparation of dual-use GPTES@ZnO photocatalyst from waste warm filter cake and evaluation of its synergic photocatalytic degradation for air-water purification

Organic pollutants are the most critical threats to the health of air and water resources. On this basis, fabricating a photocatalytic acrylic film with dual-use (i.e. removing benzene from air and MB/MO dyes from water) was aimed in this research. For this purpose, waste warm filter cake (WWFC) was used to extract zinc from it. Zinc element was separated from WWFC by a basic leaching method and acidified to prepare zinc oxide nanoparticles. In the following, a simple hydrothermal method was used to increase the surface functionality of the extracted ZnO nanoparticles in order to establish active reaction sites for reaction to silane coupling agent and increase in the holes that were prepared during photo-excitation. Thereafter, the nanoparticles were modified with 3-glycidoxypropyltriethoxysilane (GPTES) at different concentrations. The band gap of the modified nanoparticles decreased from 3.25 to 3.1 eV by surface modification. The photocatalytic performance of ZnO nanoparticles was assessed by degradation of MB and MO aqueous solution (50 ppm) under simulated UV/Visible irradiations. MB and MO were degraded 91 and 60% under UV light and 65 and 50% under visible light after 150 min of irradiation. The photo degradation rate increased after adding carboxy methyl cellulose (CMC) surfactant to methylene blue and adding cocamide-dea (CDE-G) surfactant to methyl orange. The results confirmed that the green surfactants improve the dispersion and surface interaction of the modified nanoparticles in the dyes solution and cause more electron charge transfer which creates effective photocatalytic sites. The prepared nanocomposite films were placed in a photo-reactor to remove gaseous benzene from air under UV/visible irradiation. Gas chromatography (GC) results showed that the modified nanoparticles removed up to 35.25 and 20.34% of benzene from air. Colorimetric analysis (ΔE*) showed that the acrylic film contained modified nanoparticles degraded 91 and 82% of MB, and 85 and 76% of MO under UV/visible lights, respectively. In the end, it can be said that these photocatalytic films are able to remove environmental pollution in air and water.