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The adsorption of cadmium ions by magnetite (Fe3O4)@biosilica/alginate (MBA nano-hybrid) was the main aim of the present investigation. Herein, MBA nano-hybrid was synthesized via chemical precipitation technique. As-synthesized MBA nano-hybrid was characterized using FT-IR, FESEM and XRD analyzes. Based on the results, the maximum adsorption capacity of the adsorbent for the removal of Cd(II) was obtained at the initial pH of 7.0. At the initial Cd(II) concentration of 40 mg/L, increasing the reaction time to 180 min led to the Cd adsorption of 35.36 mg/g. Since the removal of Cd(II) after the reaction time of 60 min was insignificant, the reaction time of 60 min was considered as optimum reaction time for performing the experimental runs. According to the results, Langmuir isotherm and pseudo-second order kinetic models were the best fitted models with high correlation coefficients (R2 > 0.99). The results of thermodynamic study indicated exothermic (positive ΔH°) and spontaneous nature (negative ΔG°) of the adsorption of Cd(II) on the surface of MBA nano-hybrid. Negligible reduction in the adsorption capacity of the nano-hybrid was observed (16.57%) after fifth experimental runs, indicating high reusability potential of the as-synthesized nano-hybrid adsorbent.

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This study aimed to investigate the degradability, mineralization, proposed decomposition pathway, intermediate products, and toxicity of effluent from trichlorfon (TCF) degradation in water by UV/sulfite-advanced reduction process (UV/S-ARP). This study was experimentally performed in a photochemical reactor as a batch operation. The source of light was a UV lamp. Sulfite ion was used as the reducing agent. After the treatment, the residual concentration of TCF was measured by liquid chromatography equipped with tandem mass spectrometry (LC-MS/MS). UV/S-ARP had the highest performance at an initial pH of 7, a sulfite ion concentration of 120 mg/L, a contact time of 60 min, and a TCF concentration of 10 mg/L. Under such conditions, the degradation efficiency of TCF was 96.0%, and the amount of mineralization based on the removal of TOC and COD was 74.6% and 79.5%, respectively. The results of the degradation mechanism showed that eaq- and SO3•- have played the greatest role in dechlorination and transformation of TCF. Based on the identified intermediates, more complex compounds are transformed into compounds with simpler structures by UV/S-ARP. Evaluating the toxicity of TCF by-products via ECOSAR bioassay showed that as-generated intermediates do not have acute and chronic adverse effects on fish. The results of our study indicated that the advanced reduction process could be an effective process for the purification of TCF-contaminated water.

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Herein, FeCuMg and CrCuMg layered double hydroxides (LDHs) were synthesized and their sonophotocatalytic activities toward Acid blue 113 (AB113) were compared. Sonolysis alone (only ultrasound) led to the decolorization efficiency of 13.0 %. A similar result was obtained in the case of the utilization of photolysis alone using a 10-W LED lamp (13.5 %). The adsorption process of AB113 onto both compounds was not efficient to significantly remove the target contaminant. The bandgap energy of 2.54 eV and 2.41 eV was calculated for FeCuMg and CrCuMg LDHs, respectively, indicating relatively higher photocatalytic activity of Cr-incorporated LDH than FeCuMg LDH. The sonophotocatalysis of AB113 (50 mg L-1) over CrCuMg LDH (81.1 %) was more efficient than that of FeCuMg LDH (57.3 %) within the reaction time of 60 min. Intermediate byproducts of the sonophotocatalytic decomposition of organic dye over the as-synthesized tri-metal layered sonophotocatalysts were also identified. Furthermore, the antibacterial activity of both LDHs was evaluated by the CFU technique and the MBC and MIC values were determined. The antibacterial assessment confirmed the higher antibacterial activity of CrCuMg LDH than that of FeCuMg LDH against Staphylococcus aureus (S. aureus).

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The modified multifunctional electrodes for electro-Fenton (EF) process are suggested to be promising cathodes for in situ electro-generation and activation of H2O2 to produce hydroxyl radicals (•OH). However, heterogeneous EF process still faces the challenges of limited catalytic activity and releasing of massive amounts of transition metals to the solution after removal of organic pollutants. The main aim of the present investigation was to prepare a cathode containing carbon nanotubes (CNTs) and CuFe nano-layered double hydroxide (NLDH) for degradation and mineralization of cefazolin antibiotic through electro-Fenton process. Structural and electrochemical analyses demonstrated that CuFeNLDH-CNTs nanocomposite was successfully incorporated on the surface of graphite cathode. Due to the increased formation of •OH in the reactor, the incorporation of CNTs into NLDH matrix with a catalyst loading of 0.1 g substantially improved the degradation efficiency of cefazolin (89.9%) in comparison with CNTs-coated (28.7%) and bare graphite cathode (22.8%) within 100 min. In the presence of 15 mM of ethanol, the degradation efficiency of cefazolin was remarkably decreased to 43.7% by the process, indicating the major role of •OH in the destruction of target molecules. Acidic conditions favored the degradation efficiency of cefazolin by the modified EF process. Mineralization efficiency of the bio-refractory compound was obtained to be 70.1% in terms of chemical oxygen demand (COD) analysis after 300 min. The gas chromatography-mass spectroscopy (GC-MS) analysis was also implemented to identify the intermediate byproducts generated during the degradation of cefazolin in the CuFeNLDH-CNTs/EF reactor.

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The aim of the present study was to investigate the photocatalytic performance of biochar (BC)-incorporated Zn-Co-layered double hydroxide (LDH) nanostructures in gemifloxacin (GMF) degradation as a model pharmaceutical pollutant. The as-prepared Zn-Co-LDH@BC showed high photocatalytic efficiency due to the enhanced separation of photo-generated charge carriers using cobalt hydroxide as well as inhibiting the agglomeration of LDH nanostructures by incorporation of BC. According to the results, 92.7% of GMF was degraded through photocatalysis in the presence of Zn-Co-LDH catalyst. The photocatalytic performance of BC-incorporated Zn-Co-LDH was highly dependent on the solute concentration and photocatalyst dosage. The addition of ethanol caused more inhibiting effect than that of benzoquinone (BQ), indicating the major role of •OH in decomposition of GMF compared to the negligible role of O2•-. A greater enhancement in the photocatalytic degradation of GMF was obtained when the photoreactor containing Zn-Co-LDH@BC nanostructures was oxygenated. Less than 10% drop in the removal efficiency of GMF was observed within five successive operational runs. The results of chemical oxygen demand (COD) analysis indicated the COD removal efficiency of about 80% within 200 min, indicating the acceptable mineralization of GMF. The reaction pathways were also proposed for the photocatalytic conversion of GMF under UV light irradiation.

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Powdered stone waste (PSW) obtained from a stone cutting industrial unit was applied as support for the immobilization of nano-sized ZnO to be utilized as an effective catalyst for the catalytic conversion of acetaminophen (ACE) under ultrasonication. The incorporation of ZnO nanostructures into PSW structure enhanced the specific surface area and pore volume of the as-prepared nanocompound. The change in the value of zero point of charge (pHzpc) of the PSW after being covered also demonstrated the good immobilization and distribution of ZnO nanostructures on the surface of PSW. The sonocatalysis of ACE over ZnO/PSW followed pseudo-first order kinetic (reaction rate of 2.27 × 10-2 1/min). The highest degradation efficiency of 98.1% was attained when the ZnO/PSW-contained sono-reactor was irradiated by UVC light. The presence of t-butanol led to the lowest degradation efficiency (57.7%), indicating that the sonocatalytic conversion of ACE was hydroxyl radical (OH)-dependent. Although the mineralization efficiency of ACE by the process was not excellent, bio-toxicity assessment on the effluent revealed decreasing the inhibition percent from 50.8 to 16.7% within reaction time of 240 min.

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Contamination of water resources by refractory organic pollutants is of great environmental and health concern because these compounds are not degraded in the conventional wastewater treatment plants. In recent years, sonocatalytic treatment has been considered as a promising advanced oxidation technique for the acceptable degradation and mineralization of the recalcitrant organic compounds. For this purpose, various sonocatalysts have been utilized in order to accelerate the degradation process. The present review paper provides a summary of published studies on the sonocatalytic degradation of various organic pollutants based on the application of carbon-based catalysts, including carbon nanotubes (CNTs), graphene (GR), graphene oxide (GO), reduced graphene oxide (rGO), activated carbon (AC), biochar (BC), graphitic carbon nitride (g-C3N4), carbon doped materials, buckminsterfullerene (C60) and mesoporous carbon. The mechanism of sonocatalytic degradation of different organic compounds by the carbon-based sonocatalysts has been well assessed based on the literature. Moreover, the details of experimental conditions such as sonocatalyst dosage, solute concentration, ultrasound power, applied frequency, initial pH and reaction time related to each study have also been discussed in this review. Finally, concluding remarks as well as future challenges in this research field regarding new areas of study are also discussed and recommended.

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The paper presents the results of investigations on the effectiveness and reaction rate constants of the oxidation of sulfide ions and organic sulfides in real industrial effluents from the production of bitumens (2000 mg S2- L-1) using hydrodynamic and acoustic cavitation. The content of the effluents was analysed in terms carbon disulfide, dimethyl sulfide, and di-tert-butyl disulfide concentration. A possibility of complete oxidation of sulfides by cavitation alone as well as by its combination with external oxidants such as hydrogen peroxide, ozone or peroxone was demonstrated. The oxidation time for the most effective processes is as little as 15 min. Due to the presence of sulfide ions, the effluents from the production of bitumens were oxidized at a strongly alkaline pH. The results of this study reveal the advantage of performing advanced oxidation processes (AOPs) at a basic pH. The effective degradation of sulfide ions enables performance of further degradation of organic contaminants at an acidic pH, ensuring high efficiency of treatment based, for example, on the Fenton reaction without the risk of release of hydrogen sulfide to the atmosphere. The results of this research are applicable to all kinds of caustic effluents for which the lack of possibility of pH adjustment limits their efficient treatment.

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The aim of the present investigation was the combination of ZnO nanostructures with nano-cellulose (NC) for the efficient degradation of tetracycline (TC) antibiotic under ultrasonic irradiation. The removal efficiency of 12.8% was obtained by the sole use of ultrasound (US), while the removal efficiency increased up to 70% by the US/ZnO treatment process. Due to the integration of ZnO nanostructures with NC, the removal efficiency of 87.6% was obtained within 45 min. The removal efficiency substantially decreased in the presence of tert-butyl alcohol (more than 25% reduction), indicating that radOH-mediation oxidation is responsible for the degradation of TC molecules. Peroxymonosulfate (PMS) led to the most enhancing effect on the removal of TC among percarbonate, persulfate and periodate ions. The addition of PMS caused the degradation efficiency of 96.4% within the short contact time of 15 min. The bio-toxicity examination on the basis of inhibition test conducted on activated sludge revealed diminishing the oxygen consumption inhibition percent [IOUR (%)] from 33.6 to 22.1% during the US/ZnO/NC process. Consequently, the utilization of the US/ZnO/NC process can convert TC molecules to less toxic compounds. However, longer reaction time is required for complete conversion into non-toxic substances.

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The present study was performed to sonochemically synthesize GdxZn1-xO (x=0-0.1) nanoparticles for sonocatalysis of Acid Orange 7 (AO7) in an aqueous medium. The results of X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) analysis confirmed proper synthesis of Gd-doped sonocatalyst. 5% Gd-doped ZnO nanoparticles with band gap of 2.8 eV exhibited the highest sonocatalytic decolorization efficiency of 90% at reaction time of 90 min. The effects of initial dye concentration and sonocatalyst dosage on decolorization efficiency were evaluated. In the presence of sodium sulfate, sodium carbonate and sodium chloride the decolorization efficiency decreased from 90 to 78, 65 and 56%, respectively. Among various enhancers, the addition of potassium periodate improved the decolorization efficiency from 90 to 100%. The highest decolorization efficiency was obtained at pH value of 6.34 (90%). The decolorization efficiency decreased only 6% after 4 repeated runs. Therefore, Gd-doped ZnO nanoparticles can be used as a promising catalyst for degradation of organic pollutants with great reusability potential.

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Landfill leachates contain a wide variety of pollutants such as organic matter, refractory compounds, ammonia, particulate and dissolved solids and hazardous metals requiring application of advanced and well designed treatment processes before release to the environment. The main purpose of this research was to evaluate the efficiency of combined air stripping, Fenton oxidation and biological treatment in treating landfill leachate, especially the elimination of ammonia and refractory organics. The laboratory scale set-up consisted of three sequential but separate steps. The optimum conditions for air stripping and the Fenton oxidation were determined for landfill leachate from Karaj city, Iran. The final step was a moving bed bioreactor with HRTs of 18, 12 and 6 h. The highest NH(3)-N removal was 79% in the air stripping process at pH 10.5. At the optimum conditions for the Fenton reaction at a reaction time of 90 min, pH 3 and a H(2)O(2)/Fe(2+) mass ratio of 20, the COD removal was 61% and improved the BOD/COD ratio from 0.42 to 0.78. The overall COD removal including the final biological reactor with a HRT of 6 h resulted in an effluent COD concentration of less than 100 mg L(-1).

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