Initial Reaction Time Research Articles

Advancing Antimony(III) Adsorption: Impact of Varied Manganese Oxide Modifications on Iron-Graphene Oxide-Chitosan Composites.

Antimony (Sb) is one of the most concerning toxic metals globally, making the study of methods for efficiently removing Sb(III) from water increasingly urgent. This study uses graphene oxide and chitosan as the matrix (GOCS), modifying them with FeCl2 and four MnOx to form iron-manganese oxide (FM/GC) at a Fe/Mn molar ratio of 4:1. FM/GC quaternary composite microspheres are prepared, showing that FM/GC obtained from different MnOx exhibits significant differences in the ability to remove Sb(III) from neutral solutions. The order of Sb(III) removal effectiveness is MnSO4 > KMnO4 > MnCl2 > MnO2. The composite microspheres obtained by modifying GOCS with FeCl2 and MnSO4 are selected for further batch experiments and characterization tests to analyze the factors and mechanisms influencing Sb(III) removal. The results show that the adsorption capacity of Sb(III) decreases with increasing pH and solid-liquid ratio, and gradually increases with the initial concentration and reaction time. The Langmuir model fitting indicates that the maximum adsorption capacity of Sb(III) is 178.89 mg/g. The adsorption mechanism involves the oxidation of the Mn-O group, which converts Sb(III) in water into Sb(V). This is followed by ligand exchange and complex formation with O-H in FeO(OH) groups, and further interactions with C-OH, C-O, O-H, and other functional groups in GOCS.

Efficient Removal of Tetracycline from Water by One-Step Pyrolytic Porous Biochar Derived from Antibiotic Fermentation Residue.

The disposal and treatment of antibiotic residues is a recognized challenge due to the huge production, high moisture content, high processing costs, and residual antibiotics, which caused environmental pollution. Antibiotic residues contained valuable components and could be recycled. Using a one-step controllable pyrolysis technique in a tubular furnace, biochar (OSOBs) was produced without the preliminary carbonization step, which was innovative and time- and cost-saving compared to traditional methods. The main aim of this study was to explore the adsorption and removal efficiency of tetracycline (TC) in water using porous biochar prepared from oxytetracycline fermentation residues in one step. A series of characterizations were conducted on the prepared biochar materials, and the effects of biochar dosage, initial tetracycline concentration, reaction time, and reaction temperature on the adsorption capacity were studied. The experimental results showed that at 298 K, the maximum adsorption capacity of OSOB-3-700 calculated by the Langmuir model reached 1096.871 mg/g. The adsorption kinetics fitting results indicated that the adsorption of tetracycline on biochar was more consistent with the pseudo-second-order kinetic model, which was a chemical adsorption. The adsorption isotherm fitting results showed that the Langmuir model better described the adsorption process of tetracycline on biochar, indicating that tetracycline was adsorbed in a monolayer on specific homogeneous active sites through chemical adsorption, consistent with the kinetic conclusions. The adsorption process occurred on the surface of the biochar containing rich active sites, and the chemical actions such as electron exchange promoted the adsorption process.

Adsorption of vanadium using a new anionic Schiff Base adsorbent and its application to vanadium separation from boiler ash

AbstractBackgroundThis study reports the preparation of 2‐hydroxy‐3‐(4‐(((2‐((2‐(((E)‐4‐(2‐hydroxy‐3‐(trimethylammonio)propoxy)‐3‐methoxybenzylidene)amino)ethyl)amino)ethyl)imino)methyl)‐2‐methoxyphenoxy)‐N,N,N‐trimethylpropan‐1‐aminium (HYM/QA). The adsorbent was employed to extract and concentrate vanadium from its solutions and boiler ash samples.ResultsThe impact of initial dosage, pH, reaction time and temperature on the sorption behavior of V(V) was examined. Under optimal conditions (pH 5, 0.08 g dose, 45 min at room temperature), a sorption capacity of 392.25 mg g−1 was achieved. The uptake of V(V) on HYM/QA was effectively reversed using 1 mol L−1 NaOH, regenerating the material. After six cycles of sorption and elution, the sorption capability remained at 91.4% of its initial value. The efficiency and selectivity of HYM/QA toward V5+ ions were assessed using the separation factor parameter, revealing limited interference from heavy metals such as Mn2+, Cr3+, Pb2+, Si4+, Al3+, NO32−, HCO3− and Zn2+. The uptake process of HYM/QA for V(V) conformed to the Langmuir and Dubinin–Radushkevich isotherm models and the pseudo‐second‐order kinetic model. HYM/QA was characterized by infrared, Brunauer–Emmett–Teller surface area, 1H NMR, 13C NMR and gas chromatography–mass spectrometry analyses, confirming successful preparation. Thermodynamic assessments suggested that the sorption process is endothermic, spontaneous and becoming more favorable with rising temperature.ConclusionThe optimized conditions were used to adsorb vanadium from boiler ash samples, and the obtained vanadium pentaoxide was analyzed and confirmed using various tools, demonstrating the material's effectiveness for vanadium extraction. © 2024 Society of Chemical Industry (SCI).

Response surface methodology optimization of sodium diclofenac adsorption using activated carbon derived from falcata tree sawdust

The presence of sodium diclofenac in water is a significant problem due to its adverse effects on terrestrial and aquatic organisms. Thus, this study investigated the Falcata tree sawdust as the precursor of activated carbon for the adsorption of diclofenac in an aqueous solution. The characterization of falcata tree sawdust-activated carbon (FTSAC) was evaluated by SEM and FTIR analysis. The activated falcata sawdust converted to activated carbon has a 30 % yield. The optimal values for the operating parameters, FTSAC dosage, initial sodium diclofenac concentration, reaction time and pH, were determined using the central composite design (CCD) of the response surface methodology (RSM). The optimal removal efficiency suggested by CCD is 93.98 % with the optimum conditions of parameters of 0.80 g FTSAC dosage, 200 ppm initial sodium diclofenac concentration, 20 min reaction time, and pH 4. These optimal values of parameters were validated by an actual experiment, and the result (average removal efficiency: 92.08 %) is within a 95 % confidence interval. On the other hand, the pseudo-second-order (R2 = 0.9991) kinetic model depicts the rate of absorption of FTSAC adsorbing SD. Moreover, the Langmuir-Freundlich isotherm or Sips isotherm model (R2 = 0.9904) is the best-fit model that describes the heterogeneous adsorption dynamics of FTSAC surfaces. This study indicates that falcata sawdust can serve as a promising and viable alternative raw material to produce activated carbon.

Refractory organic matter removal from mature leachate by bipolar electrocoagulation-electrooxidation reactor configurations

In this study, mature leachate treatment with combined electrochemical processes was investigated to benefit from the advantages of electrocoagulation (EC) and electrooxidation (EO) simultaneously. First, control experiments were conducted, the most effective anode-cathode combination for EO was selected as Ti/IrO2-Gr, the number of Al electrodes for EC was determined as 3 and the number of Fe electrodes was determined as 5. Optimization of process parameters of the combined system with Al and Fe electrodes was conducted with Box-Behnken design (BBD). With BBD, the effect of the process parameters (initial pH, current density, and reaction time) on the system responses (COD, UV254, and color removal efficiencies) was determined. The suitability of the created model in the study was analyzed statistically and the results of quadratic models were found compatible with experimental studies. The model's capacity for prediction was also confirmed by validation experiments under optimum conditions. By implementing the optimum conditions, COD, UV254, and color removal efficiencies were determined as 71.5 %, 60.2 %, and 93.2 %, respectively for the combined process with Al electrodes and 79.5 %, 68.0 %, and 97.7 %, respectively for the combined process with Fe electrodes. Correlation of actual and predicted data showed that BBD is reliable for optimizing process parameters of combined processes with Al and Fe electrodes. The obtained results showed that combined processes are more effective than hybrid processes, based on both pollutant removal efficiencies and energy consumption.

Optimization and kinetic analysis of electrocoagulation-assisted adsorption for treatment of young landfill leachate

An investigation was conducted on the electrocoagulation treatment of high-strength young landfill leachate using an electrode made of aluminium in a batch electrochemical cell reactor. An iron sheet of 1 m⨯1 m⨯1.1 m (L: B: H) was used to construct the two landfill simulating reactors, both the reactors were operated at different conditions, i.e., one without rainfall (S1) and the other with rainfall (S2). Both reactors have 51% wet and 49% dry waste, which is the typical waste composition of India, and the quantity of waste taken was 450 kg; hence, the generated leachate was treated. This work focuses on the utilization of electrocoagulation as the sole treatment method where coagulation and adsorption occur simultaneously for young landfill leachate. The study employed a central composite design (CCD) to systematically vary the initial pH, current density (CD), and reaction time to examine their impact on the removal efficiency of COD (Chemical oxygen demand), TOC (Total organic carbon), and TSS (Total Suspended Solids). The optimum conditions obtained were a pH of 7.35, a CD of 15.29 mA/cm2, and a reaction duration of 57 min. When the conditions were optimized, the COD, TSS, and TOC removal efficiencies were 83.56%, 73.12%, and 85.58%, respectively. Also, the electrodes depleted 2.78 g of Al/L. In addition, pseudo-first-order and pseudo-second-order kinetics were employed to examine the elimination of contaminants by adsorption on aluminium hydroxide, thereby confirming the adsorption process. After investigation through energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD), with the produced sludge confirmed that electrocoagulation removed a significant amount of metals from landfill leachate.

Improved bacterial elimination in wastewater through electrocoagulation: hydrogen generation, adsorption of colloidal bacteria-flocks, and electric field bactericidal action

ABSTRACT Electrocoagulation (EC) has emerged as a promising method for wastewater treatment, offering efficient removal of various contaminants, including bacteria. This study investigates the mechanisms underlying bacterial removal in EC processes, mainly the hydrogen-mediated foam, the effect of operational parameters, including initial pH, current density, and reaction time, and evaluates the associated energy consumption. The EC reactor employed aluminum electrodes and operated at a current intensity of 3.0 A. It demonstrated a notable bacterial removal efficiency, with 120.102 UFC ml−1 of mesophyll floral aerobic bacteria removed through colloid bacteria-flocs precipitation, 440.102 UFC ml−1 via bacterial-bulls flotation from foam, and 117.102 UFC ml−1 through attraction at the electrodes’ plate surface. We found that the EC process leads to the formation of aluminum hydroxide and ferrous hydroxide precipitates, which adsorb bacteria and facilitate their removal from the wastewater via electrostatic forces with an energy consumption of 45 kWh/m3. Overall, this research provides valuable insights into the mechanisms governing bacterial removal in EC and highlights the importance of energy consumption analysis for optimizing wastewater treatment processes.

Effective adsorption of phosphate using a Mg–Al–La composite from synthetic/real wastewater: adsorptive behaviour, column tests and economic evaluation

ABSTRACT The present study utilised an adsorbent that integrates Mg with Al and La (i.e. MAL composite) to remove low-concentration phosphate from wastewater. The adsorption properties of MAL were identified through batch experiments of phosphate removal, in which the impacts of influencing factors such as initial pH and reaction time on the phosphate adsorption by MAL adsorbent were explored. Besides, the thermodynamics and kinetics were also investigated, where the phosphate adsorption follows the pseudo-second-order kinetics, indicating that chemisorption and internal diffusion control dominate the phosphate removal. Dynamic phosphate removal by MAL adsorbent was investigated using a fixed-bed column at different adsorbent particle sizes, flow rates and temperatures, in which the breakthrough curves were simulated. The phosphate removal by MAL adsorbent was examined at practical wastewater treatment, which achieves high efficiency and thus provides a preliminary basis for the commercial use of the adsorbent. Apart from this, the techno-economic analysis of phosphate adsorption was also conducted.

Monitoring of early curing stage of cemented soil using polymer optical fiber sensors and microscopic observation

Deep cement mixing (DCM) piles are widely utilized for reinforcing soft clay foundations, particularly in coastal regions where soil stability is critical. Monitoring the quality and early-stage behavior of cemented soil is essential to ensure the effectiveness of DCM pile projects in meeting design requirements. Innovative methods for on-site monitoring are necessary to enhance the reliability and efficiency of these reinforcement techniques. In this study, a novel approach is proposed utilizing polymer optical fiber (POF) sensors based on physical optical sensing principles to monitor the initial hydration degree and overall quality of cemented soil during the early curing stage. The proposed method relies on the principle of physical optical sensing, where POF sensors are employed to measure changes in reflected light intensity (LI) and temperature in cemented soil. Two crucial variables, namely the initial water content and the amount of cement, are considered in analyzing their impact on the LI and temperature changes over time. Unconfined compressive strength (UCS) tests and scanning electron microscopy (SEM) analysis are conducted on cemented soil samples with varying water-cement ratios to investigate their mechanical properties and microstructure evolution. The results of the UCS tests indicate that higher initial water content prolongs the initial hydration reaction time required for cemented soil with different cement contents. Analysis of LI curves reveals a rapidly rising trend as the hydration reaction progresses, particularly evident in samples with higher initial water content. SEM analysis further demonstrates that a stable POF LI corresponds to the completion of the hydration process, with hydrated gel formation resulting in a more compact microstructure and smaller voids. The findings highlight the significant influence of cement quantity and initial water content on the mechanical strength and microstructure of cemented soil. By analyzing changes in reflected LI and temperature, the proposed monitoring method provides valuable insights into the early-stage behavior and quality of cemented soil during the curing process. This innovative use of POF sensors for on-site monitoring offers a novel approach to evaluating cemented soil in DCM pile projects.

Valorization of spent catalyst of sponge iron production industries into high-purity metallic nickel via a novel three-step method of leaching, cementation and purification

In the present study, a three-step flowsheet combining hydrometallurgical extraction, electrochemical recovery, and purification steps is developed to investigate the possibility of recovering high-purity metallic nickel powder from the spent catalyst of the sponge iron production industry. In the extraction step, the Response Surface Methodology (RSM) is used to study and optimize the effect of temperature (25–85 °C), time (30–120 min), acid concentration (1–5 M), and NaCl concentration (0–0.16 g/mL) on the Ni and Al extraction efficiency with the help of the Design-Expert software. The optimal conditions for extracting 100 % Ni with 1.25 % Al impurity are 75 °C, 190 min, 3 M H2SO4, and 0.13 g/mL NaCl. During the electrochemical recovery step, Ni+2 ions from the leached solution were cemented by Al powder to produce metallic nickel powder. The solution’s initial pH, temperature, reaction time, and Al particle size are the process restrictions leading to a decrease in the efficiency and purity of the nickel powder. At this step, more than 99 % of the nickel ions, with more than 98 % purity, were obtained as magnetic nickel powder using the optimal temperature of 80 °C, and solution initial pH of 0.2, by using Al powder with less than 65 μm in particle size. At these operating conditions, the Al consumption was 7.5 times greater than the stoichiometric value. In the final step, the Al impurity in the synthetic nickel powder was removed using 1.5 M sodium hydroxide for 60 min, and the nickel powder was purified to 99.9 %. The ICP, SEM, and EDS analyses were used to determine the quality of the nickel powder.

A parametric optimization for leveraging the potential of ammonia modified magnetic pine cone hydrochar for Cr (VI) contaminated wastewater treatment

The present study evaluated the biosorption potential of magnetic pine cone hydrochar (MPHC) for chromium removal from wastewater. Initially, three different methodologies were followed for the synthesizing magnetic hydrochar and were tested for chromium removal and with a maximum removal of 91.3%, ammonia-modified MPHC showed its tremendous potential for Cr (VI) removal. Further, the hydrochar was characterized physically, chemically, magnetic, and morphological and a Box-Behnken experimental design was used for examining the effect of all the five parameters for Cr (VI) removal from the simulated wastewater system. Ammonia-modified MPHC showed a removal efficiency of 98.46% under the optimized batch shake flask system with the initial chromium concentration (55 mg/L), MPHC dose (550 mg/L), temperature (40 °C) and reaction time (120 min) and iron-MPHC ratio (30%). Here, the maximum Cr (VI) adsorption capability (qe) was found to be 154 mg/g. Further, the effect of different bed height, inlet pollutant flow rate, and inlet pollutant concentration during the continuous packed bed biosorption study showed a significant removal. The breakthrough curves for Cr (VI) removal obtained via the continuous flow-through column study confirmed that MPHC in the fixed-bed column suits Cr (VI) removal.

NiTiO3 nanoparticles: An environmental game changer in electro-Fenton wastewater remediation

BackgroundIn the face of escalating water pollution challenges, the study explores the efficacy of Electro-Fenton (EF) treatment using NiTiO3 perovskite-modified cathodes for methylene blue (MB) removal from wastewater. MethodsEmploying a Central Composite Design (CCD) methodology, significant factors influencing the EF process, including initial MB concentration, pH, applied current, and reaction time, were optimized. The NiTiO3 catalyst was meticulously characterized, revealing its rhombohedral crystal structure, uniform particle distribution, and efficient charge transfer properties. FindingsElectrochemical analyses demonstrated the superior performance of the NiTiO3/Graphite electrode, emphasizing its increased electroactive sites, enhanced oxygen reduction capability, and reduced charge transfer resistance compared to the bare Graphite electrode. The EF process was finely tuned, demonstrating a 95.38 % removal efficiency of MB at optimal conditions (initial concentration: 25 mg L−1, pH: 4.5, current: 40 mA, time: 110 min). This study underscores the promising potential of NiTiO3-modified cathodes in advanced water treatment applications, highlighting their robust efficiency and environmental significance in combating persistent organic pollutants.

CO2-enhanced PET depolymerization by catalyst free methanolysis

Depolymerization shows promise as a strategy for converting waste plastic into monomers that can be used for repolymerization. However, catalytic approaches would be more complex and expensive due to catalyst separation, recovery, and recycling. Here, we present a CO2-enhanced subcritical methanolysis method without catalyst that can generate monomer from poly(ethylene terephthalate)(PET). The synergistic effect of CO2 on the subcritical methanolysis process for PET depolymerization was investigated including the CO2 initial pressure, reaction temperature and reaction time. Under subcritical conditions, the optimal reaction parameters with PET conversion ratio of 100% and DMT yield of 79.1% are as follows: temperature of 220℃, methanol to PET mass ratio of 6:1 and reaction time of 50 min. Moreover, through the analysis of experimental data, it was concluded that the depolymerization reaction follows a first-order kinetics, with the reaction rate being 2–3 times faster than the traditional process. However, the apparent activation energy for both reactions is found to be similar, with values of 135.1 kJ·mol−1 and 146.2 kJ·mol−1, respectively.

Advancements in application of modified biochar as a green and low-cost adsorbent for wastewater remediation from organic dyes.

Synthetic organic dyes, which are resistant to biodegradation, pose a notable health risk, potentially leading to cancer and respiratory infections. Researchers have addressed this concern by exploring physicochemical methods to remove organic dyes from wastewater. A particularly promising solution involves modified biochar adsorbents, which demonstrate high efficiency in organic dye removal. Biochar, a charcoal-like material derived from biomass pyrolysis, offers advantages such as low cost, eco-friendliness, high efficiency and reusability. Beyond its role in sustainable soil remediation, biochar proves effective in removing organic dyes from wastewater after undergoing physical or chemical modification. Acid-base activation or metal-heteroatom impregnation enhances biochar's adsorption capacity. This comprehensive review examines the attributes of biochar, common methods for production and modification, and the impacts of raw materials, pyrolysis temperature, heating rate and residence time. It further elucidates the biochar adsorption mechanism in the removal of organic dyes, assessing factors influencing efficiency, including biochar feedstock, solution pH, adsorption temperature, particle size, initial dye concentration, biochar dosage and reaction time. It explores challenges, opportunities, reusability and regeneration methods of biochar in treating organic dye wastewater. It also discusses recent advances in organic dye removal using adsorption-based biochar. The review ultimately advocates for enhancing biochar's adsorption performance through post-modification.

Oil absorbent based on lauryl methacrylate grafting onto cellulose of water hyacinth (Eichhornia crassipes)

AbstractIn this article, a novel oil‐absorbent polymer was synthesized by graft polymerization of lauryl methacrylate (LMA) onto water hyacinth (WH) using 2,2′‐azobisisobutyronitrile (AIBN) as initiator and divinyl benzene (DVB) as a crosslinking agent. The effects of initiator content, LMA content, reaction temperature, reaction time, and crosslinker content on the superabsorbent polymer were investigated. The prepared graft copolymer WH‐g‐LMA was analyzed using FTIR, SEM, XRD, and TGA. In the presence of the better cross‐linker DVB (1.5%) and contact time of about 25 min, the maximal Q (oil sorption capacity) of co‐polymer towards crude and Soybean oils is 23.68 and 25.72 g g−1, respectively. The Q is reduced when sorbent dosage increased, but it increases with increasing the temperature and reaches a maximum of 40 °C. The reusability of co‐polymer is characteristic of 7 sorption/desorption cycles.

In situ chemical oxidation of tinidazole in aqueous media by heat-activated persulfate: kinetics, thermodynamic, and mineralization studies

This study investigated the use of heat-activated persulfate (HAP) as a chemical oxidation technique for removing tinidazole (TNZ) antibiotic from aqueous solutions. The impact of various operating parameters, including TNZ initial concentration (20 μM), persulfate (PS) initial dose (0.2–2 mM), solution pH (3–11), solution temperature (20–60 °C), and reaction time (10–120 min), was examined. The results indicated that sulfate radicals were the primary species responsible for TNZ degradation. Higher temperatures and PS concentrations improved the process, while higher pH values and TNZ initial concentrations slowed it down. Additionally, chloride and bicarbonate ions reduced reaction rates, with chloride ions having a more significant effect. Under optimal conditions (including [TNZ]0 = 20 μM, pH = 7, [PS]0 = 1 mM, temperature = 60 °C, and reaction time = 120 min), the removal efficiency achieved was 91.15%, with a mineralization rate of 85.8%. These results suggest that the process is relatively safe. The degradation of TNZ was best described by the pseudo-first-order model compared to other models. Additionally, the process was found to be exothermic and spontaneous, with a negative Gibbs free energy change indicating that it is thermodynamically feasible. The study found HAP to be an effective and cost-efficient technique for removing TNZ antibiotic due to its ease of operation and the absence of the need for additional chemicals or waste handling. Based on these findings, HAP can be considered an advanced oxidation technique for treating antibiotic-contaminated water.

Effect and mechanism of iron-carbon micro-electrolysis pretreatment of organic peroxide production wastewater.

The wastewater from organic peroxide production has high chemical oxygen demand (COD) concentration and poor biodegradability, so it is necessary to find a cost-effective treatment method. The iron-carbon microelectrolysis (IC-ME) technology was used to pretreat the organic peroxide production wastewater, and the influence of reaction conditions on the removal effect of pollutants and the degradation mechanism were studied. The effects of initial pH, iron filings, iron-carbon ratio, and reaction time on the wastewater treatment were investigated by single-factor and response surface optimization experiments, and the degradation mechanism was analyzed by three-dimensional fluorescence spectroscopy, UV-Vis, and gas chromatography mass spectrometry (GC-MS). The experimental results showed that the COD removal efficiency was 35.67% and the biodegradability of wastewater was increased from 0.113 to 0.173 under the conditions of initial pH of 3.1, the dosage of iron filings of 30.5g/L, the ratio of iron-carbon of 1.01, and the reaction time of 122.8min, and the process of IC-ME for degrading COD of wastewater from the production of organic peroxide was consistent with the secondary reaction. The IC-ME process could decompose macromolecular organic compounds such as tyrosine proteins and aromatic proteins, and improve the biodegradability of wastewater. It provides a theoretical reference for the practical application of IC-ME to treat this type of wastewater.

RSM approach for process optimization of the photodegradation of congo red by a novel NiCo2S4/chitosan photocatalyst

The current study reported a facile co-precipitation technique for synthesizing novel NiCo2S4/chitosan nanocomposite. The photocatalytic activity of the prepared nanocomposite was evaluated using congo red (CR) dye as a target pollutant. The central composite design was employed to examine the impact of different reaction conditions on CR dye degradation. This study selected the pH, photocatalyst loading, initial CR concentration and reaction time as reaction parameters, while the degradation efficiency (%) was selected as the response. A desirability factor of 1 suggested the adequacy of the model. Maximum degradation of 93.46% of 35 ppm dye solution was observed after 60 min of visible light irradiation. The response to surface methodology (RSM) is a helpful technique to predict the optimum reaction conditions of the photodegradation of CR dye. Moreover, NiCo2S4/Ch displayed high recyclability and reusability up to four consecutive cycles. The present study suggests that the prepared NiCo2S4/chitosan nanocomposite could prove to be a viable photocatalyst for the treatment of dye-contaminated wastewater.

Tailoring photocatalytic performance through Fe-doped TiO2/ZnO for effective remediation of organic contaminants

The development of highly efficient photocatalysts holds significant promise for addressing contemporary environmental challenges. This study focuses on the synthesis and characterization of a novel photocatalyst, iron-doped TiO2/ZnO particles, created through the sol-gel technique. The incorporation of iron ions into the crystalline structure of TiO2/ZnO aims to enhance the photocatalytic efficiency of TiO2. The findings revealed that Fe–ZnO/TiO2 exhibits a more thermally stable lattice compared to TiO2/ZnO, thereby retarding the phase transformation from anatase to rutile under higher calcination temperature. The photocatalytic performance of the synthesized photocatalyst was evaluated through the degradation of methyl orange under visible light irradiation. A statistical response surface methodology based on a central composite design was employed to develop a predictive model for color removal (as the dependent variable) considering variations in irradiation intensity, initial color concentration, catalyst concentration, reaction time, and pH (as independent variables). The analysis of variance identified the initial color concentration as the most influential factor, negatively affecting the predicted response. The experimental values of color removal exhibited good agreement with the predicted values from the regression model with a coefficient of determination of 0.949, indicating the accuracy of this model in predicting the mentioned outcomes. The presented model indicated that, for a sample of methyl orange with an initial concentration of 21.97 ppm, a reaction time of 117.69 min under direct irradiation of 21.63 W, a catalyst concentration of 0.61 g/L, and a pH of 4.74, the optimal color removal efficiency of 78.99 % was achieved.

Adsorption thermodynamics and kinetics of hydrochloric-acid-modified bentonite for Zn(II) in wastewater

In order to study the Zn(II) adsorption characteristics of hydrochloric-acid-modified bentonite in wastewater, physical characterization of hydrochloric-acid-modified bentonite was carried out, the effects of the initial concentration, reaction time, and temperature on the Zn(II) adsorption were investigated, and the adsorption kinetics and thermodynamic mechanism of the hydrochloric-acid- modified bentonite adsorption of Zn(II) were examined. The results showed that hydrochloric acid modification increased the interlayer spacing of the bentonite, and the structure of the binding between slices became looser. Hydrochloric acid modification altered the hydroxyl groups on the bentonite surface, and the hydrophilicity was enhanced. The Zn(II) adsorption capacities of bentonite and hydrochloric-acid-modified bentonite increased with the increase in the initial Zn(II) concentration, and the adsorption followed the Langmuir and Freundlich equations. The thermodynamic parameters suggested that the adsorption of Zn(II) was an endothermic, spontaneous, and entropy-increasing process. The adsorption basically reached equilibrium within 120 min, and the adsorption followed the quasi-second-order adsorption kinetic equation. The adsorption process was mainly chemical adsorption, and the intra-particle diffusion process was not the only step controlling the adsorption rate. This study provides a theoretical basis for the remediation of toxic metal wastewater and contaminated soil.