Optimization the Effects of Physicochemical Parameters on the Degradation of Cephalexin in Sono-Fenton Reactor by Using Box-Behnken Response Surface Methodology

The utility of ultraviolet beam in advanced oxidation-reduction processes: a review on the mechanism of processes and possible production free radicals

Advanced oxidation processes (AOPs) and advanced reduction processes (ARPs) are a set of chemical treatment procedures designed to eliminate organic (sometimes inorganic) contamination in water and wastewater by producing free reactive radicals (FRR). UV irradiation is one of the factors that are effectively used in oxidation-reduction processes. Not only does the UV beam cause the photolysis of contamination, but it also leads to the product of FRR by affecting oxidants-reductant, and the pollutant decomposition occurs by FRR. UV rays produce active radical species indirectly in an advanced redox process by affecting an oxidant (O3, H2O2), persulfate (PS), or reducer (dithionite, sulfite, sulfide, iodide, ferrous). Produced FRR with high redox potential (including oxidized or reduced radicals) causes detoxification and degradation of target contaminants by attacking them. In this review, it was found that ultraviolet radiation is one of the important and practical parameters in redox processes, which can be used to control a wide range of impurities.

Aqueous degradation of 6-APA by hydroxyl radical: a theoretical study

CONTEXT

Degradation reactions of micropollutants such as antibiotics with OH radicals are very important in terms of environmental pollution. Therefore, in this study, the degradation kinetic mechanism of 6-aminopenicillanic acid (6-APA) with OH radical was investigated by density functional theory (DFT) methods.

METHODS

For the calculations, different functionals such as B3LYP, MPW1PW91, and M06-2X were used with a 6-31 g(d,p) basis set. The aquatic effect on the reaction mechanism was investigated by conductor-like polarizable continuum model (CPCM). For the degradation kinetics in aqueous media, the addition of explicit water molecules was also calculated. Subsequent reaction mechanism for the most probable reaction product was briefly discussed.

RESULTS

Among the functionals used, B3LYP results were consistent with the experimental results. Calculated kinetic parameters indicated that the OH-addition path was more dominant than the H-abstraction paths. With the increase of explicit water molecules in the models, the energy required for the formation of transition state complexes decreased. The overall rate constant is calculated as 2.28 × 10¹¹ M^-1 s^-1 at 298 K for the titled reaction.

Photocatalytic degradation of industrial dye using hybrid filler impregnated poly-sulfone membrane and optimizing the catalytic performance using Box-Behnken design

Mixed Matrix Membranes have gained significant attention over the past few years due to their diverse applications, unique hybrid inorganic filler and polymeric properties. In this article, the impregnation of nano-hybrid filler (polyoxometalates (∼POMs) encapsulated into the metal-organic framework (MOF) ∼ PMOF) on the polysulfone membrane (∼PSF) was done, resulting in a mix matrix membrane (∼PMOF@PSF). The developed structure was characterized by Fourier transform infrared (FT-IR), powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and transmission electron microscopes (TEM). The results confirmed that the nano-hybrid filler was successfully fabricated on the surface of PSF. Different loading ratios of nano-hybrid filler (5%, 10%, 20%, 30%, and 40%) were used for impregnation. The study's objective was to enhance catalytic performance using optimization curves designed using a three-level Box-Behnken Design (BBD) simulation. The photodegradation of Methylene Blue (∼MB) was studied against PMOF@PSF_30% and was found to perform optimally when the concentration of catalyst, time of degradation, and temperature were 0.05-0.15 gm, 40-120 min, and 30-70 °C respectively. These experiments were replicated 15 times, and obtained results were further processed using a two-quadratic polynomial model to develop response surface methodology (RSM), which allowed for a functional relationship between the decolorization and experimental parameters. The optimal performance of the reaction mixture was calculated to be 0.15 gm for concentration, 70 °C for temperature, with an 80 min reaction time. Under these optimal conditions, the predicted decolorization of MB was 98.09%. Regression analysis with R² > 0.99 verified the fit of experimental results with predicted values. The PMOF@PSF PSF_30% demonstrated excellent reusability as its dye degradation properties were significantly unaffected after ten cycles.

Mechanism analysis of hydroxypropyl guar gum degradation in fracture flowback fluid by homogeneous sono-Fenton process

An effective hybrid system was applied as the first report for the successful treatment of key pollutants (hydroxypropyl guar gum, HPG) in fracturing flowback fluid, and the synergistic index of the hybrid system was 20.45. In this regard, chemical oxygen demand (COD) removal ratio was evaluated with various influencing operating factors including reaction time, H2O2 concentration, Fe2+ concentration, ultrasonic power, initial pH, and temperature. The optimal operating parameters by single-factor analysis method were: the pH of 3.0, the H2O2 concentration of 80 mM, the Fe2+ concentration of 5 mM, the ultrasonic power of 180 W, the ultrasonic frequency of 20-25 kHz, the temperature of 39 ℃, the reaction time of 30 min, and the COD removal rate reached 81.15 %, which was permissible to discharge surface water sources based on the environmental standards. A possible mechanism for HPG degradation and the generation of reactive species was proposed. Results of quenching tests showed that various impacts of the decomposition rate by addition of scavengers had followed the order of EDTA-2Na < BQ < t-BuOH, therefore OH radicals had a dominant role in destructing the HPG. Based on the kinetic study, it was concluded that Chan Kinetic Model was more appropriate to describe the degradation of HPG. Identification of intermediates by GC-MS showed that a wide range of recalcitrant compounds was removed and/or degraded into small molecular compounds effectively after treatment. Under the optimal conditions, the sono-Fenton system was used to treat the fracturing flowback fluid with the initial COD value of 675.21 mg/L, and the COD value decreased to 80.83 mg/L after 60 min treatment, which was in line with the marine sewage discharge standard. In conclusion, sono-Fenton system can be introduced as a successful advanced treatment process for the efficient remediation of fracture flowback fluid.

Possibilities and Limitations of the Sono-Fenton Process Using Mid-High-Frequency Ultrasound for the Degradation of Organic Pollutants

Mid-high-frequency ultrasound (200-1000 kHz) eliminates organic pollutants and also generates H₂O₂. To take advantage of H₂O₂, iron species can be added, generating a hybrid sono-Fenton process (sF). This paper presents the possibilities and limitations of sF. Heterogeneous (a natural mineral) and homogeneous (Fe²⁺ and Fe³⁺ ions) iron sources were considered. Acetaminophen, ciprofloxacin, and methyl orange were the target organic pollutants. Ultrasound alone induced the pollutants degradation, and the dual competing role of the natural mineral (0.02-0.20 g L^-1) meant that it had no significant effects on the elimination of pollutants. In contrast, both Fe²⁺ and Fe³⁺ ions enhanced the pollutants' degradation, and the elimination using Fe²⁺ was better because of its higher reactivity toward H₂O₂. However, the enhancement decreased at high Fe²⁺ concentrations (e.g., 5 mg L^-1) because of scavenger effects. The Fe²⁺ addition significantly accelerated the elimination of acetaminophen and methyl orange. For ciprofloxacin, at short treatment times, the degradation was enhanced, but the pollutant complexation with Fe³⁺ that came from the Fenton reaction caused degradation to stop. Additionally, sF did not decrease the antimicrobial activity associated with ciprofloxacin, whereas ultrasound alone did. Therefore, the chemical structure of the pollutant plays a crucial role in the feasibility of the sF process.

Statistical modeling optimization for antibiotics decomposition by ultrasound/electro-Fenton integrated process: Non-carcinogenic risk assessment of drinking water

The present work proposes an ultrasound (US) assisted electro-Fenton (EF) process for eliminating penicillin G (PNG) and ciprofloxacin (CIP) from aqueous solutions and the process was further optimized by response surface methodology (RSM)- Box-Behnken design (BBD). The impact of pH, hydrogen peroxide (H₂O₂) concentration, applied voltage, initial pollutant concentration, and operating time were studied. The capability application of the electro-Fenton (EF) and US processes was compared separately and in combination under the optimum conditions of pH of 4, a voltage of 15 V, the initial antibiotic concentration of 20.7 mg/L, H₂O₂ concentration of 0.8 mg/L, and the operating time of 75 min. The removal efficiency of PNG and CIP using the sono-electro-Fenton (SEF) process, as the results revealed, was approximately 96% and 98%, respectively. The experiments on two scavengers demonstrated that ^⦁OH contributes significantly to the CIP and PNG degradation by SEF, whereas ^⦁O^-₂ corresponds to only a negligible amount. The total organic carbon (TOC) and chemical oxygen demand (COD) analyses were used to assess the mineralization of CIP and PNG. The efficiency of COD and TOC removal was reached at 73.25% and 62.5% for CIP under optimized operating circumstances, and at 61.52% and 72% for PNG, respectively. These findings indicate that a sufficient rate of mineralization was obtained by SEF treatment for the mentioned pollutants. The reaction kinetics of CIP and PNG degradation by the SEF process were found to follow a pseudo-first-order kinetic model. In addition, the human health risk assessment of natural water containing CIP and PNG that was purified by US, EF, and SEF processes was done for the first time. According to the findings, the non-carcinogenic risk (HQ) caused by drinking purified water by all three systems was calculated in the acceptable range. Thus, SEF is a proper system to remove various antibiotics in potable water and reduces their human health risks.

Efficient removal of antibiotics from water resources is a public health priority: a critical assessment of the efficacy of some remediation strategies for antibiotics in water

This review discusses the fundamental principles and mechanism of antibiotic removal from water of some commonly applied treatment techniques including chlorination, ozonation, UV-irradiation, Fenton processes, photocatalysis, electrochemical-oxidation, plasma, biochar, anaerobicdigestion, activated carbon and nanomaterials. Some experimental shortfalls identified by researchers such as certain characteristics of degradation agent applied and the strategies explored to override the identified limitations are briefly discussed. Depending on interactions of a range of factors including the type of antibiotic compound, operational parameters applied such as pH, temperature and treatment time, among other factors, all reviewed techniques can eliminate or reduce the levels of antibiotic compounds in water to varying extents. Some of the reviewed techniques such as anaerobic digestion generally require longer treatment times (up to 360, 193 and 170 days, according to some studies), while others such as photocatalysis achieved degradation within short contact time (within a minimum of 30, but up to 60, 240, 300 and 1880 minutes, in some cases). For some treatment techniques such as ozonation and Fenton, it is apparent that subjecting compounds to longer treatment times may improve elimination efficiency, whereas for some other techniques such as nanotechnology, application of longer treatment time generally meant comparatively minimal elimination efficiency. Based on the findings of experimental studies summarized, it is apparent that operational parameters such as pH and treatment time, while critical, do not exert sole or primary influence on the elimination percentage(s) achieved. Elimination efficiency achieved rather seems to be due more to the force of a combination of several factors.

Cephalexin degradation initiated by OH radicals: theoretical prediction of the mechanisms and the toxicity of byproducts

In this work, the density functional theory is used to study the local reactivity of cephalexin (CLX) to radical attack and explain the mechanism of the reaction between CLX and hydroxyl radical attack leading to degradation byproducts. The reaction between •OH and CLX is supposed to lead to either an addition of a hydroxyl radical or an abstraction of a hydrogen. The results showed that the affinity of cephalexin for addition reactions increases as it passes from the gas to the aqueous phase and decreases as it passes from the neutral to the ionized form. Thermodynamic data confirmed that OH addition radicals (R_add) are thermodynamically favored over H abstraction radicals (R_abs). The ecotoxicity assessments of CLX and its byproducts are estimated from the acute toxicities toward green algae, Daphnia, and fish. The formation of byproducts is safe for aquatic organisms, and only one byproduct is harmful to Daphnia.

Ligustrum lucidum Leaf Extract-Assisted Green Synthesis of Silver Nanoparticles and Nano-Adsorbents Having Potential in Ultrasound-Assisted Adsorptive Removal of Methylene Blue Dye from Wastewater and Antimicrobial Activity

Present study was conducted to investigate the adsorption and ultrasound-assisted adsorption potential of silver nanoparticles (AgNPs) and silver nanoparticles loaded on chitosan (AgCS composite) as nano-adsorbents for methylene blue (MB) removal. AgNPs were synthesized using leaf extract of Ligustrum lucidum, which were incorporated on the chitosan’s surface for modification. UV−Vis Spectroscopy, FTIR, XRD, SEM, and EDX techniques were used to confirm the synthesis and characterization of nanomaterials. Batch adsorption and sono-adsorption experiments for the removal of MB were executed under optimal conditions; for fitting the experimental equilibrium data, Langmuir and Freundlich’s isotherm models were adopted. In addition, the antimicrobial potential of the AgNPs and AgCS were examined against selected bacterial and fungal strains. UV−Vis spectroscopy confirmed AgNPs synthesis from the leaf extract of L. lucidum used as a reducer, which was spherical as exposed in the SEM analysis. The FTIR spectrum illustrated phytochemicals in the leaf extract of L. lucidum functioning as stabilizing agents around AgNPs and AgCS. Whereas, corresponding crystalline peaks of nanomaterial, including a signal peak at 3 keV indicating the presence of silver, were confirmed by XRD and EDX. The Langmuir model was chosen as an efficient model for adsorption and sono-adsorption, which exposed that under optimum conditions (pH = 6, dye initial concentration = 5 mg L−1, adsorbents dosage = 0.005 g, time = 120 min, US power 80 W), MB removal efficiency of AgNPs was >70%, using ultrasound-assisted adsorption compared to the non-sonicated adsorption. Furthermore, AgNPs exhibited promising antibacterial potential against Staphylococcus aureus with the maximum zone of inhibition (14.67 ± 0.47 mm). It was concluded that the green synthesis approach for the large-scale production of metallic nanoparticles is quite effective and can be recommended for efficient and cost-effective way to eradicate dyes, particularly from textile wastewater.

Decontamination of toxic Malathion pesticide in aqueous solutions by Fenton-based processes: Degradation pathway, toxicity assessment and health risk assessment

This study evaluates the degradation efficiency of Malathion using Fenton (Fe²⁺/H₂O₂: F), photo-Fenton (UV/Fe²⁺/H₂O₂: PF), and sono-photo Fenton (US/UV/Fe²⁺/H₂O₂: SPF) processes as well as determines the toxicity of the byproducts of degradation. The effect of various operational parameters on the Malathion degradation rate, including pH, Fe²⁺ concentration, Malathion concentration, and H₂O₂ were studied. The removal efficiency was determined to be 98.79% for the SPF, > 70.92% for the PF, and > 55.94% for the F processes under the following optimal conditions: pH = 3, [H₂O₂]₀ = 700 mg/L, [Fe²⁺]₀ = 20 mg/L, and [Malathion]₀ = 20 mg/L. The operating costs (USD/kg_{Malathion-removed}) were acquired as SPF > PF > F. Moreover, Malaoxon, diethyl maleate, diethyl malate, ethyl 2-hydroxysuccinate, and D-malate were among the detected byproducts from the Malathion degradation in the SPF process. Both the non-carcinogenic risk and the carcinogenic risk were assessed to establish the quality of the effluent from all three processes. The toxicity of the treated effluents, determined by Vibrio fischeri luminescence, indicated that the toxicity depends on the selected treatment process. The high degradation efficiency of the Fenton-based processes is not equivalent to achieving detoxification of the effluents. As such, the SPF process was determined to be the most effective for the Malathion degradation, total organic carbon (TOC) removal, and health risk assessment.

Synthesis of Atmospherically Stable Zero-Valent Iron Nanoparticles (nZVI) for the Efficient Catalytic Treatment of High-Strength Domestic Wastewater

Here, we report the fabrication of nZVI by the wet chemical technique in the presence of ethanol using ferric iron and sodium borohydride as the reducing agents under ambient conditions. The obtained nZVI particles are mainly in a zero-valent oxidation state and do not undergo significant oxidation for several weeks. The structural and morphological parameters of nZVI were investigated by using UV, XRD, SEM, EDX, TEM, and DLS analysis. The optical nature, bandgap energy, and absorption edge were all revealed by the UV–visible spectrum. The phase development and crystallinity of nZVI particles were shown by the XRD pattern. The morphological investigation revealed that the nanoparticles were spherical with an average size of 34–110 nm by using ImageJ software, and the elemental analysis was analyzed using EDX. Furthermore, the catalytic treatment performance of domestic wastewater was evaluated in terms of pH, COD (chemical oxygen demand) solubilization, total solids (TS), volatile solids (VS), phosphorous, and total nitrogen (TN) reduction under aerobic and anaerobic operating conditions. The effluent was subjected to a process evaluation with a different range (100–500 mg/L) of nZVI dosages. The COD solubilization and suspended solids reduction were significantly improved in the anaerobic condition in comparison to the aerobic condition. Furthermore, the effect of nZVI on phosphorous (PO43−) reduction was enhanced by the electrons of iron ions. The high concentration of nZVI dosing has a positive impact on COD solubilization and phosphorous removal regardless of the aeration condition with 400 mg/L of nZVI dosage.

Novel catalytic degradation of Diazinon with ozonation/mg-Al layered double hydroxides: optimization, modeling, and dispersive liquid-liquid microextraction

PURPOSE

In this study MgAl- layered double hydroxides (MgAl-LDH) nanoparticles were prepared by a simple and fast co-precipitation method and used as a catalyst in the ozonation process to degrade diazinon from aqueous solutions.

METHODS

The structure of the synthesized MgAl-LDH was investigated by X-ray diffraction pattern (XRD) and field emission scanning electron microscope-energy dispersive spectroscopy (FESEM-EDX). The response surface methodology (RSM) was used to investigate the effects of different parameters including of reaction time, initial diazinon concentration, pH, and LDH dose on the removal of diazinon by MgAl-LDH catalytic ozonation process. Central Composite Design (CCD) was employed for the optimization and modeling of the process. Dispersive liquid-liquid microextraction (DLLME) method was used to extract diazinon from aqueous samples. The GC-Mass analysis was performed to determine intermediate compounds during diazinon degradation reactions. To evaluate the process performance, TOC and COD removal were measured under optimum conditions.

RESULTS

The highest removal efficiency of 92% was observed in optimum conditions as follow; initial diazinon concentration: 120 mg/L, pH: 8.25, LDH dose: 750 mg/L, and reaction time: 70 min. The quadratic model was obtained with a good fit. The removal of COD and TOC were 80% and 74%, respectively.

CONCLUSION

This process can be suggested and used in the treatment of various industrial wastewaters.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40201-021-00687-w.

Elimination of cephalexin and doxycycline under low frequency ultrasound

Cephalexin (CPX) and doxycycline (DOX) are two of the most used antibiotics to treat bacterial infections in human medicine, veterinary practices, animal husbandry, agriculture, aquaculture, among others. Nevertheless, due to their excessive consumption and incomplete absorption during their metabolization, they have been detected in different environmental matrices and the effluents of wastewater treatment plants, which reflects that conventional water treatment methods are not enough to eliminate this type of compounds. This paper presents the main results about the removal of the antibiotics CPX and DOX under low frequency (40 kHz) ultrasonic radiation (US). The effects of operational parameters such as the solution initial pH and the applied US power were assessed considering the response surface methodology and a face centered, central composite experimental design. The results indicated that evaluated operational factors significantly affect the pollutants elimination and that US technology is able to remove them completely. In addition, in terms of mineralization, experimental results showed a reduction of the organic carbon present in the solutions and a significant increase of ions (nitrates and sulfates) concentration, suggesting that part of the organic matter was transformed into CO₂, H₂O and inorganic species. Finally, results regarding the samples toxicity indicated that ultrasonic treatment could promote a significant reduction in this parameter, and the potential negative effect associated to CPX and DOX presence in water bodies.

Sustainable approaches for removal of cephalexin antibiotic from non-clinical environments: A critical review

In this article, the removal of cephalexin (CFX) antibiotic from non-clinical environment is reviewed. Adsorption and photocatalytic degradation techniques are widely used to remove CFX from waters and wastewaters, the combination of these methods is becoming more common for CFX removal. The treatment methods of CFX has not been reviewed before, the present article aim is to organize the scattered available information regarding sustainable approaches for CFX removal from non-clinical environment. These include adsorption by nanoparticles, bacterial biomass, biodegradation by bacterial enzymes and the photocatalysis using different catalysts and Photo-Fenton photocatalysis. The metal-organic frameworks (MOFs) appeared to have high potential for CFX degradation. It is evident from the recently papers reviewed that the effective methods could be used in place of commercial activated carbon. The widespread uses of photocatalytic degradation for CFX remediation are strongly recommended due to their engineering applicability, technical feasibility, and high effectiveness. The adsorption capacity of the CFX is ranging from 7 mg CFX g^-1 of activated carbon nanoparticles to 1667 mg CFX g^-1 of Nano-zero-valent iron from Nettle. In contrast, the photo-degradation was 45% using Photo-Fenton while has increased to 100% using heterogeneous photoelectro-Fenton (HPEF) with UVA light using chalcopyrite catalyst.

The optimization of enzymatic oxidation of levofloxacin, a fluoroquinolone antibiotic for wastetwater treatment

The global presence of antibiotics in the environment has created concerns about the emergence of antibiotic resistance bacteria and potential hazard to humans and the ecosystem. This work aims to study the removal of levofloxacin, a new generation fluoroquinolone antibiotic from aqueous solutions by enzyme mediated oxidation process and optimization of the conditions thereof by response surface methodology (RSM) using Box-Behnken design (BBD). For this study, experiments were conducted to analyze the effect of independent variables namely, pH, temperature, mediator concentration and antibiotic concentration on the degradation percentage of levofloxacin antibiotic using laccase enzyme derived from Trametes versicolor. The residual levofloxacin concentration was determined using high performance liquid chromatography (HPLC). On applying the quadratic regression analysis, among the main parameters, it was found that the percentage degradation was significantly affected by all the four variables. The predicted values for percentage degradation of levofloxacin were close to the experimental values obtained and the R² (0.95) indicated that the regression was able to give a good prediction of response for the percentage degradation of levofloxacin in the studied range. The optimal conditions for the maximum degradation (99.9%) as predicted by the BBD were: temperature of 37 °C, pH of 4.5, mediator concentration of 0.1 mM and levofloxacin concentration of 5 μg mL^-1. The findings of the study were further extended to study the effect of partially purified enzymes isolated from Pleurotus eryngii, Pleurotus florida and Pleurotus sajor caju on the degradation of levofloxacin at concentrations ranging from as low as 0.1 to as high as 50 µg mL^-1 in synthetic wastewater utilizing the optimized conditions generated by BBD. A maximum degradation of 88.8% was achieved with the partially purified enzyme isolated from Pleurotus eryngii at 1 µg mL^-1 levofloxacin concentration which was at par with the commercial laccase which showed 89% degradation in synthetic wastewater at the optimized conditions. The biodegradation studies were conducted using only 2 units of laccase. Thus, the expensive commercial laccase can be effectively replaced by crude laccase isolated from indigenous macrofungi such as P. eryngii, P. florida and P. sajor caju as a cost effective alternative to degrade levofloxacin present in contaminated wastewater using as low as 2 units of enzyme for a 72 h treatment period.

Optimization of Fenton Technology for Recalcitrant Compounds and Bacteria Inactivation

In this work, the Fenton technology was applied to decolorize methylene blue (MB) and to inactivate Escherichia coli K12, used as recalcitrant compound and bacteria models respectively, in order to provide an approach into single and combinative effects of the main process variables influencing the Fenton technology. First, Box–Behnken design (BBD) was applied to evaluate and optimize the individual and interactive effects of three process parameters, namely Fe2+ concentration (6.0 × 10−4, 8.0 × 10−4 and 1.0 × 10−3 mol/L), molar ratio between H2O2 and Fe2+ (1:1, 2:1 and 3:1) and pH (3.0, 4.0 and 5.0) for Fenton technology. The responses studied in these models were the degree of MB decolorization (D%MB), rate constant of MB decolorization (kappMB) and E. coli K12 inactivation in uLog units (IuLogEC). According to the results of analysis of variances all of the proposed models were adequate with a high regression coefficient (R2 from 0.9911 to 0.9994). BBD results suggest that [H2O2]/[Fe2+] values had a significant effect only on D%MB response, [Fe2+] had a significant effect on all the responses, whereas pH had a significant effect on D%MB and IuLogEC. The optimum conditions obtained from response surface methodology for D%MB ([H2O2]/[Fe2+] = 2.9, [Fe2+] = 1.0 × 10−3 mol/L and pH = 3.2), kappMB ([H2O2]/[Fe2+] = 1.7, [Fe2+] = 1.0 × 10−3 mol/L and PH = 3.7) and IuLogEC ([H2O2]/[Fe2+] = 2.9, [Fe2+] = 7.6 × 10−4 mol/L and pH= 3.2) were in good agreement with the values predicted by the model.

Modeling of chromium (VI) removal from aqueous solution using modified green-Graphene: RSM-CCD approach, optimization, isotherm, and kinetic studies

BACKGROUND

The aim of this study was to investigate the removal of Cr (VI) using Green-Graphene Nanosheets (GGN) synthesized from rice straw.

METHODS

Synthesis of the GGN was optimized using response surface methodology and central composite design (CCD). The effect of two independent variables including KOH-to-raw rice ash (KOH/RRA) ratio and temperature on the specific surface area of the GGN was determined. To have better removal of Cr (VI), GGN was modified using the grafting amine group method. In the Cr (VI) removal process, the effects of four independent variables including initial Cr (VI) concentration, adsorbent dosage, contact time, and initial solution pH were studied.

RESULTS

The results of this study showed that the optimum values of the KOH/RRA ratio and temperature for the preparation of GGN were 10.85 and 749.61 °C, respectively. The maximum amount of SSA obtained at optimum conditions for GGN was 551.14 ± 3.83 m 2 /g. The optimum conditions for Cr (VI) removal were 48.35 mg/L, 1.46 g/L, 44.30 min, and 6.87 for Cr (VI) concentration, adsorbent dosage, contact time, and pH, respectively. Based on variance analysis, the adsorbent dose was the most sensitive factor for Cr (VI) removal. Langmuir isotherm (R2 = 0.991) and Pseudo-second-order kinetic models (R2 = 0.999) were the best fit for the study results and the Q max was 138.89 mg/g.

CONCLUSIONS

It can be concluded that the predicted conditions from the GGN synthesis model and the optimum conditions from the Cr (VI) removal model both agreed with the experimental findings.

A comprehensive study on the application of FeNi3@SiO2@ZnO magnetic nanocomposites as a novel photo-catalyst for degradation of tamoxifen in the presence of simulated sunlight

Pharmaceutical compounds at trace concentrations are found in the environment, especially in drinking water and food, posing significant negative effects on humans as well as on animals. This paper aimed to examine the diagnostic catalytic properties and efficacy of a novel synthesized photocatalyst, namely FeNi₃@SiO₂@ZnO magnetic nanocomposite, for the removal of tamoxifen (TMX) from wastewater under simulated sunlight. According to the results, it was found that TMX was completely degraded operating under optimized conditions (i.e. pH = 7, catalyst dose = 0.01 g/L, initial TMX concentration = 20 mg/L and reaction time = 60 min). The reaction kinetics of TMX degradation followed a pseudo-first order kinetics model. The final by-products from the TMX photodegradation were water, carbon dioxide, acetic acid, nitroacetic acid methyl ester, 2-methyl-2-pentenal, and 4-methyl-2-pentanol. In addition, the synthesized photocatalyst could successfully performed five consecutive photodegradation cycles. The obtained results revealed that the synthesized FeNi₃@SiO₂@ZnO magnetic nanocomposite holds a great potential to be applied as a photocatalyst for the degradation of TMX on an industrial scale.

The practical utility of the synthesis FeNi3@SiO2@TiO2 magnetic nanoparticles as an efficient photocatalyst for the humic acid degradation

Humic acid (HA) compounds in drinking water and wastewater disinfection processes are viewed as precursors of highly toxic, carcinogenic, and mutagenic disinfection by-product chemicals. In recent times, these compounds have gained considerable attention of scientists for their successful removal from aqueous solutions to permissible limits. To achieve this aim, the present study investigated, for the first time, the photocatalytical performance of the synthesis FeNi₃@SiO₂@TiO₂ nanoparticles for the HA degradation under different environmental conditions. The photocatalytic reactions were performed using ultraviolet (UV) radiation, whose intensity was fixed at 2500 μW/cm² throughout the experimental study. The characterization study performed, using specific diagnostic techniques, revealed the presence of several good morphological, magnetic, and catalytic specifications of the synthesized nanoparticles. The use of the simplified form of the Langmuir-Hinshelwood equation sufficiently describes the experimental data of the HA kinetic degradation, as it shows a high coefficient of regression values. Furthermore, the complete HA degradation was reached under conditions of pH = 3; initial HA concentration = 10 mg/L; FeNi₃@SiO₂@TiO₂ nanoparticles dosage = 0.01 g/L; and reaction time >30 min. Thus, the results obtained from this research suggested that the catalyst of FeNi₃@SiO₂@TiO₂ nanoparticles was an attractive, novel, and effective agent, which could be used for the degradation of HA in the photocatalytic processes.

Catalytic Oxidation Process for the Degradation of Synthetic Dyes: An Overview

Dyes are used in various industries as coloring agents. The discharge of dyes, specifically synthetic dyes, in wastewater represents a serious environmental problem and causes public health concerns. The implementation of regulations for wastewater discharge has forced research towards either the development of new processes or the improvement of available techniques to attain efficient degradation of dyes. Catalytic oxidation is one of the advanced oxidation processes (AOPs), based on the active radicals produced during the reaction in the presence of a catalyst. This paper reviews the problems of dyes and hydroxyl radical-based oxidation processes, including Fenton's process, non-iron metal catalysts, and the application of thin metal catalyst-coated tubular reactors in detail. In addition, the sulfate radical-based catalytic oxidation technique has also been described. This study also includes the effects of various operating parameters such as pH, temperature, the concentration of the oxidant, the initial concentration of dyes, and reaction time on the catalytic decomposition of dyes. Moreover, this paper analyzes the recent studies on catalytic oxidation processes. From the present study, it can be concluded that catalytic oxidation processes are very active and environmentally friendly methods for dye removal.