Pseudo-first Order Kinetic Model Research Articles

Predicting the bioavailability of nitro polycyclic aromatic hydrocarbons in sediments: ZIF-8/h-BN solid-phase microextraction versus Tenax extraction

The occurrence of nitrated polycyclic aromatic hydrocarbons (NPAHs) in sediments has been widely reported, but research on NPAH bioavailability is lacking. In this study, a self-made zeolite imidazolate framework-8/hexagonal boron nitride (ZIF-8/h-BN) solid-phase microextraction (SPME) fiber and commercial Tenax are compared as efficient tools to predict the bioavailability of NPAHs in sediments with bioassays using Cipangopaludina chinensis. During the process of SPME, the NPAH concentrations on the ZIF-8/h-BN fibers reached extraction equilibrium after 72 h. The fiber extraction of NPAHs in sediments was well-fitted by the pseudo first-order kinetic model with a rate constant of 2 × 10−2 h−1 (R2 > 0.98). The extraction rates ranking of NPAHs in sediments was 2-nitrobiphenyl>1-nitropyrene>5-nitroacenaphthene>2-nitrofluorene. Compared with SPME, NPAH concentrations reached equilibrium after 168 h for the Tenax extraction. The orders of magnitude of fast, slow, and very slow desorption rate constants were 10−1, 10−2, and 10−4, respectively. At extraction equilibrium (168 h), the SPME was close to the bioavailability of the NPAHs in sediments to Cipangopaludina chinensis with a slope statistically approximated to one. In addition, the linear regression for SPME (R2 = 0.7285) was slightly higher than that of the Tenax extraction (R2 = 0.7168) over a short time (6 h). This could be because the coating material of ZIF-8/h-BN can rapidly adsorb freely dissolved NPAHs, and the SPME fibers can accurately predict the bioaccumulated concentrations of NPAHs in exposed organisms by measuring the concentration of NPAHs in the pore water of sediment. This study provides a time-saving and easy procedure to predict the bioavailability of NPAHs in sediments.

Complexes of terpyridine scaffold as efficient photocatalysts for the degradation of methylene blue pollutant in wastewater effluents

In the present protocol, a series of varyingly substituted terpyridine-based ligands have been designed and synthesized. The synthesized ligands were coordinated with different transition metal cations. Their complexation with Fe(II), Co(II) and Zn(II) led to interesting coordination compounds which for the first time, were evaluated for their photocatalytic potential against the degradation of methylene blue. Almost all the tested complexes 1–9 exhibited fascinating photocatalytic properties. However, noteworthy, photocatalytic results revealed that zinc complexes 1 ([Zn (4′-(p-tolyl)-2,2′:6′,2″-terpyridine)(SO4)2−]), 4 ([Zn (N,N-Dimethyl-4-(2,2′:6′,2″-terpyridin-4′-yl)aniline)(SO4)2−]) & 7 ([Zn (N,N-Diphenyl-4-(2,2′:6′,2″-terpyridin-4′-yl)aniline)(SO4)2−]) have high potential against the degradation of methylene blue followed by iron complexes 3 ([Fe(4′-(p-tolyl)-2,2′:6′,2″-terpyridin)2](PF6)2), 6 ([Fe(4′-(N,N-Dimethyl-4-(2,2′:6′,2″-terpyridin-4′-yl)aniline)2]2PF6) &9 ([Fe(N,N-Diphenyl-4-(2,2′:6′,2″-terpyridin-4′-yl)aniline)2]2PF6) and then cobalt complexes 2 (Co(4′-(p-tolyl)-2,2′:6′,2″-terpyridin)2](PF6)2), 5 ([Co(4′-(N,N-Dimethyl-4-(2,2′:6′,2″-terpyridin-4′-yl)aniline)2]2PF6) &8 ([Co(N,N-Diphenyl-4-(2,2′:6′,2″-terpyridin-4′-yl)aniline)2]2PF6). Among all the complexes, maximum degradation efficiencies were observed for complex 1 (67.31 %) and complex 7 (65.91 %). The optimized photocatalytic conditions were found to be 10 mg/L of initial concentration of dye solution, 20 mg of catalyst dose, pH = 4 and irradiation time of 40 min. At optimized conditions complex 7 was found to be more efficient photocatalyst with rate constant value of 0.011 min−1 as compared to the rate constant value of 0.009 min−1 for complex 1. Both complexes followed the pseudo-first order kinetics model. The reusability test indicated only 8.62 % and 7.01 % loss of photocatalytic activity for complex 1 and complex 7, respectively, up to four cycles of photodegradation reflecting that these catalysts can be used again and again. This study suggested the remarkable potential of terpyridine metal complexes for the environmental remediation to remove harmful pollutants from aqueous bodies.

TiO2/Bi2O3/PANI nanocomposite materials for enhanced photocatalytic decontamination of organic pollutants

• TiO 2 /Bi 2 O 3 /PANI nanocomposites were synthesized. • Materials characterized for structural, morphological and optical characteristics. • Nanocomposites employed for RhB and Triclopyr photocatalytic degradation. • Close contact between TiO 2 , Bi 2 O 3 and PANI promotes interfacial charge transfer. • holes are the prominent ROS for the degradation of RhB; holes and O 2 ∙ - for TC. In this present work, TiO 2 /Bi 2 O 3 /PANI nanocomposites were synthesized and employed as photocatalyst for the degradation of organic pollutants i.e. Rhodamine B dye and Triclopyr pesticides. TiO 2 /Bi 2 O 3 /PANI nanocomposites were characterized with the help of various advanced instrumentation techniques including X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), photoluminescence (PL), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) analysis. The absorption in the visible wavelength region (λ > 400 nm) increased with increasing PANI amount accompanied by π → π ∗ transition. The close contact between TiO 2 , Bi 2 O 3 and PANI promotes the interfacial charge transfer and significantly improved photocatalytic performance under the irradiation of visible LEDs. Among the prepared nanocomposites, the sample containing 5 wt. % PANI of TiO 2 /Bi 2 O 3 (TB(15)) was found to be most efficient photocatalyst and stable even after four cyclic runs for the degradation of organic pollutants. TB(15)/PANI(5) exhibited the lowest PL intensity, indicating the minimum reunion in the photoproduced electron-hole pairs, which was favorable to improve the efficiency of the photocatalyst for the removal of organic pollutants. The photodegradation rate of RhB and TC using TB(15)/PANI(5) photocatalyst reached to 99.6 % in 50 minutes and 76.1 % in 120 minutes under the visible LEDs irradiation respectively. Kinetics analysis of photocatalytic reaction obeys the pseudo first-order kinetic model with respect to concentration of organic pollutants with a regression coefficient value in the range of 0.941-0.999. The trapping experiments confirmed that holes are prominent species for the degradation of RhB, and holes and superoxide anion radical for photocatalytic degradation of TC. Finally, the mechanism of photocatalytic degradation using TiO 2 /Bi 2 O 3 /PANI nanocomposite was also proposed.

Comparison of membrane fouling induced by protein, polysaccharide and humic acid under sodium and calcium ionic conditions

To further compare the effect of sodium and calcium on the membrane fouling mechanism of typical organic matters, the adsorption behavior of sodium alginate, humic acid and bovine serum albumin on PVDF membranes were explored by quartz crystal microbalance and dissipation (QCM-D), while the adhesion force between foulants and between the foulants and membrane were examined by using atomic force microscopy (AFM) detection with foulant-coated probes. Results demonstrated that the adhesion force between organic and membrane had significant impact on the adsorption rate at the initial fouling stage, whereas the interaction force among the organic was connected with the degree of irreversible fouling and the structure of the fouling layer. Ca2+ made organic fouling more severe and irreversible due to the complexation effect under the same ionic strength conditions, which is consistent with the XDLVO theory. Compared to the other two organics, BSA demonstrated deposition more in mass, higher in adsorption rate and irreversibility under both Ca2+ and Na+ conditions, which attributed to stronger interaction forces among BSA molecules and the thus formed denser fouling layer. During the adsorption process the pseudo-second-order agreed well with fouling behavior of SA and BSA, while HA conformed to the pseudo-first order kinetic model.

Nonthermal plasma-irradiated polyvalent ferromanganese binary hydro(oxide) for the removal of uranyl ions from wastewater

Nonthermal plasma (NTP) irradiation was employed to adjust the morphological structures and valence distribution of ferromanganese (Fe–Mn)-based binary hydro (oxide) to enhance the heterogeneous adsorption of uranyl ions. The output voltage and the liquid-plate distance played a more vital role among the NTP factors in the irradiation system in influencing the polyvalent Fe–Mn binary hydro (oxide) (poly-Fe-Mn). The formation of plates, flakes, and nanoscale nodules was specifically observed, which caused more pores and fractures in the poly-Fe-Mn binary hydro (oxide). The poly-Fe-Mn performed explicitly better in the adsorption of uranium ions in comparison with the counterpart of the Fe–Mn, which was appropriately fitted by the pseudofirst-order kinetic and Elovich models. Maximum equilibrium adsorption capacities of 663.92 and 923.45 mg/g were obtained for the Fe–Mn and poly-Fe-Mn binary hydro (oxides) toward U ions in the orthogonal design, respectively. The maximum monolayer adsorption capacity achieved by the fitting of the Langmuir model was 1091.10 mg/g. Both physisorption and chemisorption contributed to the heterogeneous process of the poly-Fe-Mn toward uranium ions. The employment of NTP irradiation changed the monolayer adsorption of the traditional Fe–Mn materials and diversified the reaction mechanisms between the interface of the Fe–Mn materials and uranium ions. The elements, including O, N, and U exhibited higher compatibility and overlapped in the samples. The highly effective capture of uranium ions from the solution by the poly-Fe-Mn binary hydro (oxide) was mainly related to the chemical deposition of O and N radicals.

On the applicability of triazine-based covalent organic polymer as adsorbent for dye removal from aqueous solution

Triazine-based covalent organic polymer, TCOP, is synthesized via the reaction between cyanuric chloride and piperazine in 1,4-dioxane, and is characterized with FT-IR, EDX, elemental mapping, XRD, SEM, TEM and N2 adsorption/desorption techniques. The capability of TCOP in the removal of different types of dye pollutants is studied and it was found that the removal efficiency is more than 70% for all of them. The kinetics and equilibrium adsorption of Rhodamine B (RhB) was studied at different conditions. Most of the adsorption takes place in less than 20 min and the maximum adsorption capacity is 153 mg/g. The adsorption isotherm can be well described by the modified Langmuir-Freundlich equation and the adsorption kinetics follows the fractal-like pseudo-first order kinetics model. Both of the fitted models reveal the heterogeneity of adsorbent. The adsorption thermodynamics parameters were calculated and interpreted. Finally, it was shown that the prepared TCOP can be used for the removal of dye mixture from aqueous solution.

Synthesis of novel carbon-supported iron oxide sorbents for adsorption of dye from aqueous solutions: equilibrium and flow-through studies

Textile effluents contain dyes that negatively affect water bodies and inhibit photosynthesis by reducing sunlight penetration. This study investigated the adsorption capacity of an iron oxide sorbent immobilised on naturally derived carbon foam for the removal of organic methylene blue dye from water. In this study, the carbon precursor and iron oxide precursor were mixed and carbonised in a single vessel. Baking and carbonization of the natural grain combination produce a porous structure that can act as an effective support for the iron oxide particles. The carbon foam prepared had a self-assembled structure with flour as a basic element. Sorbents of 6 weight (wt)%, 15 wt% iron, and a 0 wt% iron control sample were prepared. Transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) techniques were used to examine the synthesised carbon foam physical properties and surface morphology. The adsorption capabilities were investigated in batch tests by determining the effects of an increase in iron content, sorbent dosage, contact time, and dye concentration. Breakthrough curves were obtained by varying the height of the sorbent bed and varying the flowrate of the dye solution. A higher bed height corresponds to a greater amount of adsorbent. The breakthrough and equilibrium adsorption capacities were found to increase with increasing bed height. When the flow rate is high, the dye solution leaves the column before equilibrium, resulting in shorter breakthrough and saturation times. Higher bed heights and lower flow rates resulted in optimal dye removal in the flow through the system. Breakthrough time increases with increasing iron content. The 15 wt% iron sample displayed superior adsorption capabilities than the 6 wt% sample, while the 0 wt% iron control sample displayed minimal adsorptive capabilities. The pseudo-first order kinetic model was the best fit model for this study (R2 > 0.96), and the adsorption equilibrium is best described by the Freundlich isotherm (R2 > 0.99). The results showed that an iron oxide sorbent immobilised on carbon foam made from natural sources is a good adsorbent for removing methylene dye.

Ficus-mediated green synthesis of manganese oxide nanoparticles for adsorptive removal of malachite green from surface water

The extract of ficus leaves was used to prepare manganese (IV) oxide nanoparticles (MnO2 NPs) for the first time. Several different analytical techniques were used to characterize the prepared MnO2 NPs. MnO2 has spherical crystals that are ~ 7 nm on average in size and have 149.68 m2/g of surface area and 0.91 cm3/g of total pore volume. Malachite green (MG) dye was then taken out of the water by adsorption using MnO2 NPs. Optimization of various adsorption parameters resulted in 188.68–277.78 mg/g maximum adsorption capacities at 298–328 K tested temperatures and 99.6% removal of 50 mg/L MG within 90 min using MnO2 dose of 0.01 g at pH 10 and 298 K. The results were tested using pseudo-first order, pseudo-second order, intraparticle diffusion, Elovich, and Liquid film kinetic models as well as Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherm models. The most likely models to describe the adsorption process at 298 K are pseudo-second-order kinetics (R2 = 0.997) with a rate constant of 4 × 10−4 g/(mg.min) and Langmuir isotherm (R2 = 0.973). Additionally, the positive values of enthalpy change (3.91–67.81 kJ/mol) and the negative values of Gibb’s free energy (− 3.38 to − 19.7 kJ/mol) indicate that the process is endothermic, spontaneous, and thermodynamically feasible. MnO2 NPs sustained their adsorption efficiency at 90.4% after 5 sorption cycles. MnO2 appears to be more selective for MG in studies examining the adsorption of various cationic dyes. Lately, the biosynthesized MnO2 NPs can be utilized to remove MG from aqueous solutions effectively.

Photodegradation of doxycycline in water induced by TiO2-MCM-41. Kinetics, TOC evolution and reusability

UV-VIS spectroscopy was used as a fast, easy-implementation and novel method to monitor and quantify the photodegradation kinetics of the emergent pollutant doxycycline (DXC) in water. TiO2 nanoparticles (NPs), bare and supported on MCM-41 type silica (TiO2-MCM-41), were used as catalysts, with the silica used in order to enhance the polydispersion of the NPs. pH played a crucial role in both, the decomposition rate and the mechanism, i.e., via hydroxyl radicals at alkaline pH or presumably via hydroperoxyl radicals at acidic pH. At constant pH, the photodegradation efficiency strongly increased as initial DXC concentration and MCM-41 loadings decreased. All data were well fitted using a pseudo first-order kinetic model. The effects of such variables on the DXC mineralization and the stability of the catalyst after UV irradiation were also studied and discussed. TiO2-MCM-41 resulted highly effective after three times reuse.

Adsorption, oxidation, kinetic and thermodynamic studies of methyl orange by magnetic Fe3O4 NPs and their chitosan/alginate nanocomposites

ABSTRACT Magnetic iron oxide (Fe3O4) nanoparticles, iron oxide chitosan (Fe3O4-CS) and iron oxide alginate (Fe3O4-AT) nanocomposite beads were synthesised using green synthesis method. They were used as both adsorbents for the adsorption of methyl orange (MO) dye from the wastewater and heterogeneous catalysts for the catalytic wet peroxidation (CWPO) of MO. While the dye removal was successfully performed with Fe3O4NPs, Fe3O4-CS and Fe3O4-AT in both adsorption studies and CWPO, the highest removal efficiency (99%) in the shortest time (8 min for adsorption, 20 min for CPWO) was obtained with Fe3O4-CS for MO removal. The adsorption experiments were performed with the batch techniques at different contact time, pH, initial dye concentration, temperature, amount of adsorbent and foreign ion effect parameters by Fe3O4-CS adsorbent. The equilibrium was quickly reached after 30 min at pH 3 and 298 K. Fitting equilibrium data to Langmuir, Temkin and Freundlich isotherms showed that Langmuir model was more suitable to describe MO adsorption with a maximum monolayer adsorption capacity of 132 mg/g at 298 K. The Experimental data were analysed using intra particle diffusion, pseudo-first-order and pseudo-second-order kinetic models and it was found that the adsorption kinetics followed a pseudo-second-order equation. Based on thermodynamic studies, adsorption process occurred as spontaneous and exothermic. The effects of the amount of catalyst, pH, temperature and H2O2 concentration were investigated to determine their catalytic activities for the decomposition of MO with CWPO technique. The reusability of Fe3O4-CS for both adsorption and CWPO techniques for MO removal was performed, and the adsorption and oxidation efficiency was found to be 97%. Moreover, the reaction kinetics was also investigated and the oxidation reaction was in good agreement with the pseudo-first order kinetic model. The activation energy (Ea) of the reaction was found to be 10.72 kJ/mol.

Fabrication and Characterisation of MWCNT/Polyvinyl (PVC) Polymer Inclusion Membrane for Zinc (II) Ion Removal from Aqueous Solution.

Heavy metal pollution has prompted researchers to establish the most effective method to tackle the impacts of heavy metals on living things and the environment, which include by applying nanoparticles. An example is the employment of multi-walled carbon nanotubes (MWCNTs) as an additive in an intermediate membrane or polymer inclusion membrane (PIM). The MWCNTs were added to enhance the properties and reinforce the transport performance of zinc (II) ion (Zn2+) removal from the source phase to the receiver phase by the PIMs. The present study constructed a membrane with a poly(vinyl chloride) (PVC)-based polymer, dioctyl phthalate (DOP) plasticiser, and bis-(2-ethylhexyl) phosphate (B2EHP) carrier incorporated with different concentrations of MWCNTs. The contact angle (CA), water uptake, ion exchange capacity (IEC), and porosity of the fabricated membranes were evaluated. The membrane was also characterised by employing scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and electrochemical impedance spectroscopy (EIS). Subsequently, the fabricated PIM (W1) and mixed matrix (MM)-PIM (W2–W5) samples were assessed under different parameters to acquire the ideal membrane composition and effectiveness. Kinetic modelling of Zn2+ removal by the fabricated PIMs under similar conditions was performed to reveal the mechanisms involved. The average removal efficiency of the membranes was >99% at different parameter conditions. Nevertheless, the W3 membrane with 1.0 wt% MWCNT immersed in a 5 mg/L initial Zn2+ concentration and 1.0 M receiver solution for seven hours at pH 2 demonstrated the highest percentage of Zn2+ removal. The experimental data were best fitted to the pseudo-first-order kinetic model (PFO) in kinetic modelling, and the permeability and flux of the W3 at optimum conditions were 0.053 m s−1 and 0.0532 mol m−2 s−1, respectively. In conclusion, the transport mechanism of Zn2+ was enhanced with the addition of the MWCNTs.

Fabrication of PbO2 Electrodes with Different Doses of Er Doping for Sulfonamides Degradation.

In the present study, PbO2 electrodes, doped with different doses of Er (0%, 0.5%, 1%, 2%, and 4%), were fabricated and characterized. Surface morphology characterization by SEM-EDS and XRD showed that Er was successfully doped into the PbO2 catalyst layer and the particle size of Er-PbO2 was reduced significantly. Electrochemical oxidation of sulfamerazine (SMR) in the Er-PbO2 anode system obeyed te pseudo first-order kinetic model with the order of 2% Er-PbO2 > 4% Er-PbO2 > 1% Er-PbO2 > 0.5% Er-PbO2 > 0% PbO2. For 2% Er-PbO2, kSMR was 1.39 h−1, which was only 0.93 h−1 for 0% PbO2. Effects of different operational parameters on SMR degradation in 2% Er-PbO2 anode system were investigated, including the initial pH of the electrolyte and current density. Under the situation of an initial pH of 3, a current density of 30 mA·cm−2, a concentration of SMR 30 mg L−1, and 0.2 M Na2SO4 used as supporting electrolyte, SMR was totally removed in 3 h, and COD mineralization efficiency was achieved 71.3% after 6 h electrolysis. Furthermore, the degradation pathway of SMR was proposed as combining the active sites identification by density functional calculation (DFT) and intermediates detection by LC-MS. Results showed that Er-PbO2 has great potential for antibiotic wastewater treatment in practical applications.

Adsorption of Frequently Used Antibiotics From Contaminated Water Using Peanut Shells

The removal of pharmaceutical contaminants from water using cost-efficient and environmentally friendly adsorbents has proven to be extremely effective. The adsorption of amoxicillin (AMX) and tetracycline (TET) from wastewater using peanut shells (PS) were described in this study. The PS was characterized using Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray (EDX) techniques. The pH at the point of zero charge (pHpzc) of PS was determined to be 6.5. The influence of operating parameters such as pH, time, initial concentration, adsorbent mass and temperature on the adsorption were evaluated. The adsorption data best fit the Sips isotherm with R2 value of 0.999 for both AMX and TET and the maximum adsorption capacities of PS were obtained to be 42.47 mg g-1 for TET and 61.44 mg g-1 for AMX. Adsorption data were found to fit the pseudo first-order kinetic model for both AMX and TET. Thermodynamic parameters ΔG, ΔH and ΔS were determined to be 3.86, -8.88 and -41.36 for TET adsorption and -2.74, -16.64 and -45.15 for AMX adsorption. The negative ΔH values show that both adsorptions were exothermic while the ΔG values show that the adsorption was spontaneous for AMX and non-spontaneous for TET. The results show peanut shells is effective for the removal of AMX and TET from wastewater.

Neutral red dye adsorption on carbon nano-onions: viability assay interference and adduct characterisation

Carbon nano-onions (CNO) are versatile carbon nanomaterials with many potential biomedical applications. In this work, the interaction of submerged arc discharge in water (SADW) produced CNOs with the neutral red (NR) dye was studied. This dye is used in the in vitro toxicity NR assay, one of the most commonly used dye-based procedures to determine cell viability. Firstly the NR assay was carried out in murine fibroblast cell cultures exposed to CNOs. It was demonstrated that this assay produced invalid results due to the strong adsorption of NR on the CNOs. Fourier transform infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS) studies confirmed the effective adsorption of the NR on CNOs and π-π stacking as the main interaction between them. The adsorption of NR on the CNOs was evaluated by studying the decrease of the dye solution absorbance. The influence of different experimental conditions such as pH and CNOs dosage was evaluated: absorbance was found to diminish with the CNO dosage. For the maximum dosage used of 240 μg ml−1, the highest absorbance drops of −85% at pH 7 and −78% at pH 4 were registered. The adsorption process was found to be described best by a pseudo-first order (PFO) kinetics model (R 2 = 0.99), with a kinetic adsorption constant of k 1 = 0.02 min−1 and achieving an estimated sorption capacity of 3866 mg of dye per gram of CNOs. This is one of the highest values ever reported for dyes’ adsorption on carbon materials. Lastly, density functional theory (DFT) calculations were carried out to gain further insights into the interaction. These studies suggest a CNO highest occupied molecular orbital (HOMO)/NR lowest unoccupied molecular orbital (LUMO) electron density transfer as the main orbital interaction.

Removal of the Amoxicillin antibiotic from aqueous matrices by means of an adsorption process using Kaolinite clay

With the hеlp of a Κaolinite clay adsorbеnt, this study examined the fеasibility of removing Αmoxicillin antibiotic from aquеous solutions. The effects of various operational parameters which affect the elimination procеss were studied as adsorbent dosage (1–3 g.L−1), initial pΗ (3.0–8.5) and temperature (23–48 °C), in addition, the kinetics and adsorption isotherms were also evaluated by different modеls in order to evaluate the pеrformance and adsorption mechanisms of Αmoxicillin. The results show that the equilibrium betweеn the antibiotic and the Κaolinite clay was reachеd in 20 min, the maximum adsorption capacity of 26 mg.g−1 was achieved with an initial pH of 5.33, the amount absorbеd of the studied pollutant increased with contact time and initial antibiotic concentration, but decreased with adsorbent dosage and temperaturе. Τhe kinetic studies indicatеd that the adsorption of Αmoxicillin on Κaolinite clay can be very well fitted by a pseudo-first order kinetic model. Τhe еquilibrium data were best described by a Freundlich, suggesting adsorption onto a heterogeneous Κaolinite clay surface, where the strongеst binding sites are occupied first. Τhe adsorption capacity of Κaolinitе clay makes it a promising adsorbеnt for industrial applications and environmental protection.

Surface Chitosan-coated Fe3O4 immobilized lignin for adsorbed phosphate radicals in solution

The design of green, efficient, and conveniently recyclable biomass-based adsorbents is of great importance, but little has been reported. Therefore, magnetic Fe3O4 doped lignin-chitosan based microspheres (CS-Li@Fe3O4) was prepared by emulsion crosslinking for phosphate removal in water. The prepared CS-Li@Fe3O4 shows a spherical structure with a diameter of 5–40 µm. Benefiting from its unique morphological structure and the abundant functional groups on the surface, CS-Li@Fe3O4 exhibits excellent phosphate adsorption capacity and is applicable in environments with a pH of 2–10. More importantly, the CS-Li@Fe3O4 retains excellent adsorption capacity after 6 adsorption/desorption cycles, demonstrating remarkable recyclability and stability. The adsorption isotherm was well described by the Langmuir model, the adsorption kinetics accords with the pseudo-first order kinetic model, which indicates that the adsorption process is monolayer chemisorption. Hence, CS-Li@Fe3O4 holds promising future for water remediation owing to its green raw material and excellent phosphate capture properties.

Enhanced degradation of atrazine through UV/bisulfite: Mechanism, reaction pathways and toxicological analysis

Atrazine residue in the environment continues to threaten aquatic ecosystem and human health owing to its adverse effect. However, limited researches focused on degradation mechanism of atrazine by UV/bisulfite, especially risk of intermediates at cellular and molecular level has not been seriously elaborated. In current work, transformation patterns and residual toxicity of intermediates of atrazine by UV/bisulfite were systematically investigated. The atrazine degradation was described by a pseudo first-order kinetic model (Kobs = 0.1053 min−1). The presence of H2PO4−, HCO3− and HA had a powerful inhibition. Scavenging test of radicals illustrated that SO4•−, •OH and O2•− existed in UV/bisulfite system, SO4•− and •OH were mainly responsible for atrazine degradation. Eight degradation intermediates were identified, which were involved in dealkylation, alkyl oxidation, dechlorination-hydroxylation, and alkylic-hydroxylation. E. coli as a model microorganism was selected to assess the risk of degradation intermediates. The levels of reactive oxygen species, MDA and Na+/K+-ATPase were declined, suggesting that oxidative damage induced by these intermediates was weakened. According to differential metabolites expression analysis, several key metabolites including aspartate, L-tryptophan, L-asparagine, cytidine, cytosin, stearic acid, behenic acid, were up-regulated, and glutathione, cadaverin, L-2-hydroxyglutaric acid and phytosphingosine were downregulated, clarifying that effective detoxification of atrazine can be performed by UV/bisulfite.

Fabrication of a magnetite hydroxyapatite nanocomposite for the removal of Paraquat dichloride: Adsorption studies

Paraquat dichloride (PQ) is a broad-spectrum herbicide that is widely employed in traditional agricultural practices due to its fast activity, minimal expense and resulting in high productivity. But its uncontrolled and inappropriate usage with subsequent discharge has resulted in contamination of water bodies. It is known to pose serious threat to human well-being and to the aquatic community on account of its toxic nature. Adsorption on account of its ease of operation, cost-effectiveness and environment friendliness is recognized as one of the best tertiary treatment methods and hence can be recommended for the eradication of PQ from aqueous water bodies. The utilization of adsorbent materials with reasonable and eco-accommodating attributes is a possible answer for getting safe water. To maintain sustainability, a nanocomposite of hydroxyapatite and magnetite (NC) was fabricated and its adsorption potential for the eradication of PQ was evaluated. NC was characterised using FTIR and XRD methods. Batch adsorption studies were carried out to evaluate the extent of adsorption. For the adsorption of PQ onto NC, the effects of operating parameters such as pH, adsorbent dose, initial adsorbate concentration, contact time, and temperature were also investigated. The Langmuir model best fit the adsorption data, and the maximum adsorption capacity for PQ at 25 °C was 416.67 mg/g. The dynamics of the process were best explained by a pseudo-first order kinetic model. According to kinetic studies, equilibrium was reached within 130 min of contact time in which approximately 90 % of PQ was eradicated. Adsorption of PQ onto NC was found to be a favourable, spontaneous, and exothermic reaction by thermodynamic analysis. The present study thus demonstrates the effectiveness of fabricated nanocomposite for the eradication of PQ from aqueous solution.

Study on ultrasonic enhanced ozone oxidation of cyanide-containing wastewater

Gold smelting wastewater contains cyanide ions and copper ions, which may cause potential risks to the environment. In this study, a new ultrasonic enhanced ozone (US/O3) oxidation method was developed for the comprehensive treatment of cyanide-containing wastewater, destruction of cyanide and further recovery of copper. The cyanide removal rate and copper recovery rate reached 99.96 % and 99.3 % under the optimum conditions of ozone flow rate of 80 L/h, temperature of 25 °C, reaction time of 15 min and ultrasonic power density of 80 W/L, respectively. The dried sediment was characterized by XRD, SEM and particle size analysis, the results showed that the dry sediment was Cu slag. The experimental results were in accordance with the pseudofirst-order kinetic model with apparent rate constants of 0.1662 L/(mg·min) and 0.2056 L/(mg·min) for ozone oxidation and ultrasonic enhanced ozone (US/O3) oxidation, respectively. The mechanism of ultrasonic enhanced ozone was studied by FT-Raman, FT-IR, EPR and Gas chromatography. Ultrasonic enhanced ozone (US/O3) oxidation process for treatment of cyanide containing wastewater is characterized by rapid and complete decomposition of cyanide in wastewater and efficient recovery of valuable element copper.

Metal(loid)s removal by zeolite-supported iron particles from mine contaminated groundwater: Performance and mechanistic insights

Iron-based materials have been widely investigated because of their high surface reactivity, which has shown potential for the remediation of metal(loid)s in groundwater. However, the disadvantages of structural stability and economic feasibility always limit their application in permeable reactive barrier (PRB) technology. In this study, zeolite-supported iron particles (Zeo-Fe) were synthesized by an innovative low-cost physical preparation method that is suitable for mass production. The removal efficiency and mechanism of typical metal(loid)s (Pb2+, Cd2+, Cr6+ and As3+) were subsequently investigated using various kinetic and equilibrium models and characterization methods. The results of scanning electron microscopy and energy dispersive spectrometry (SEM-EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) confirmed that zero valent iron (Fe0) and oxidation product (Fe3O4) were successfully loaded and efficiently dispersed on zeolite. The synthesized Zeo-Fe exhibited excellent adsorption and redox capacities for the cations Pb2+, Cd2+ and anions Cr6+, As3+. The increase in the pH resulting from Fe0 corrosion also enhanced the precipitation of Fe-metal(loid)s. The maximum removal capacity for Pb2+, Cd2+, Cr6+ and As3+ was up to 70.00, 9.12, 2.35 and 0.36 mg/g, respectively. The removal processes were well described by the pseudo-second-order kinetic model for Pb2+ and Cd2+, Lagergren pseudo first-order kinetics model for As3+ and double phase first order kinetics model l for Cr6+. Cr6+ was rapidly reduced to Cr3+ by the Fe0 stabilized on Zeo-Fe, and the oxidation of As3+ to As5+ was attributed to the Fe0/Fe2+ oxidation process at the interface over time, which was further demonstrated by the mineral phase and element valence analyses of reacted Zeo-Fe. The removal mechanism for metal(loid)s was a combination of physical and chemical processes, including adsorption, co-precipitation and reduction-oxidation. Conclusively, Zeo-Fe has been shown to have potential as an effective and economical material for removing various metal(loid)s used in PRB.