Point Of Zero Charge Research Articles

Efficiencies and mechanisms of steel slag with ferric oxides for removing phosphate from wastewater using a column filter system.

The current study aimed to investigate the efficiencies and mechanisms of slag filter media for removing phosphorus from synthetic wastewater. The steel slag with high ferric oxides (Fe2O3) was subjected for the electric arc furnace (EAF) and selected as the filter media (HFe). The chemical characteristics of HFe were determined using pH, point of zero charge (PZC) and XRF. The phosphorus removal efficiency was studied in a designed vertical steel slag column rock filters in unaerated HFe (UEF) and aerated HFe (AEF) system. The microstructure of HFe was analyzed by FTIR, XRD and SEM-EDX analysis. The results of XRF revealed that ferric oxide (Fe2O3) ranged from 26.1 to 38.2%. PZC for Filter HFe was recorded at pH 10.55 ± 0.27. The highest efficiencies were recorded by UEF and AEF systems at pH 3 and pH 5 (89.97 ± 4.02% and 79.95 ± 6.25% at pH 3 and 72.97 ± 8.38% and 66.00 ± 12.85% at pH 5 for UEF and AEF, respectively). These findings indicated that AEF exhibiting higher removal than UEF systems might be due to presence high Fe concentration in AEF which play important role in the phosphorus removal. The main elements available on the surface of HFe included carbon, oxygen, iron, calcium, magnesium, silicon, platinum, sulphur, manganese, titanium and aluminium. The XRD analysis indicated that the precipitation of orthophosphate as calcium and iron-phosphates was the removal mechanism as confirmed using FT-IR analysis. These findings demonstrated the efficiency of HFe in removing of phosphorus from wastewater.

Nano-magnetically modified activated carbon prepared by oak shell for treatment of wastewater containing fluoride ion

In this study, the adsorption of fluoride ion (F-) from synthetic wastewater was performed using activated carbon/Fe3O4 nanocomposite in a batch system. To prepare activated carbon (AC), oak shell was used. Also, several analyses such as BET, SEM, EDX, FTIR, XRD, VSM and DLS analyzes were used to study the structure and morphology of the AC/Fe3O4 nanocomposite. BET analysis indicated that the specific surface area of Fe3O4 and AC/Fe3O4 were 65.44 and 226.78 m2/g, respectively, which shows the surface area of the AC/Fe3O4 composite was significantly increased compared to Fe3O4. Also, the particle size of the AC/Fe3O4 composite was obtained 75 nm by the DLS analysis. The sorption tests indicated that the highest sorption efficiency of fluoride ion using the Fe3O4/AC nanocomposite was obtained 97.4%. Moreover, the experimental results were well fitted with the Freundlich model. The maximum monolayer uptake capacity using the AC/Fe3O4 was obtained as 454.54 mg/g and showed a remarkable adsorption capacity, whichever achieved for fluoride ion sorption. Also, zero-point charge of pH (pHzpc) was obtained 5. Furthermore, the kinetic data were described by the quasi-second-order model. Besides, the thermodynamic parameters showed that the uptake of fluoride ion with the AC/Fe3O4 nanocomposite was spontaneous, practical, and endothermic. The outcomes suggest that AC/Fe3O4 nanocomposite can be effectively applied for the F- ion removal from synthetic wastewater.

Effective sequestration of Cr (VI) from wastewater using nanocomposite of ZnO with cotton stalks biochar: modeling, kinetics, and reusability.

The disposal of chromium (Cr) containing wastewater in surface water bodies without prior treatment is a serious threat to humans, animals, and plants. A novel nanocomposite (CSB/ZnO) of cotton stalks biochar (CSB) with ZnO nanoparticles was synthesized for the removal of Cr (VI) ions from contaminated water at batch scale. The impact of adsorbent dosage (1-4 g/L), initial Cr (VI) levels (25-200 mg/L), pH (2-8), and interaction time (0-180 min) was assessed for the removal of Cr (VI) from contaminated water. The Fourier-transform infrared (FTIR), scanning electron microscopy (SEM), and point of zero charge (PZC) characterization showed successful impregnation of ZnO particles on CSB with improved surface characteristics. The maximum adsorption (qmax) of CSB and CSB/ZnO was 54.95 and 107.53 mg Cr/g, respectively that is relatively higher than various previously studied adsorbents. The experimental isothermal data better fitted with the Freundlich model in comparison with other isotherm models while adsorption kinetics well corroborated with the pseudo-second-order model. The results revealed that doping of biochar with metallic nanoparticles (CSB/ZnO) proved very effective (99.6% at 50 mg/L) with high reusability (91%) after five adsorption/desorption cycles and seems a suitable strategy for the decontamination of Cr (VI) contaminated waters.

Iron and zirconium modified luffa fibre as an effective bioadsorbent to remove arsenic from drinking water

Porous luffa plant fibre (LF) was grafted with Fe and Zr, and the ability of the fabricated adsorbents to remove arsenate (As(V)) from water was investigated in batch and column adsorption experiments. The Langmuir adsorption capacity (mg g−1) at pH 7 of LF was found to be 0.035, which increased to 2.55 and 2.89 after being grafted with Fe (FLF-3) and Zr (ZLF-3), respectively. Grafting with Fe and Zr increased the zeta potential and zero point of charge (ZPC) of LF (from pH 3.9 to 7.4 for Fe grafting and to 7.6 for Zr grafting), due to chemical bonding of the metals, possibly with the hydroxyl and carboxylic groups in LF as indicated in FTIR peaks. Zeta potential and ZPC decreased after As adsorption owing to inner-sphere complexation mechanism of adsorption. The increase of pH from 3 to 10 progressively reduced the adsorbents’ adsorption capacity. Co-existing anions weakened the As(V) removal efficiency in the order, PO43− > SiO32− > CO32− > SO42−. Adsorption kinetics data fitted well to the Weber and Morris model, which revealed initial fast and subsequent slow rates of intra-particle As diffusion into the bigger pores and smaller pores, respectively. Column adsorption data fitted well to the Thomas model with the predicted adsorption capacities in the same order as in the batch adsorption experiment (ZLF-3 > FLF-3 > LF).

Nanostructured Mg substituted Mn-Zn ferrites: A magnetic recyclable catalyst for outstanding photocatalytic and antimicrobial potentials

With recently increasing the environmental problems and expected energy crisis, it is necessary to synthesis a low-cost, efficient, and UV-light responsive photocatalyst for contaminants’ degradation. The nanostructured spinel ferrite Mn0.5Zn0.5-xMgxFe2O4 NPs (x = 0.0, 0.125, 0.25, 0.375 and 0.50) were synthesized via the sol-gel method. The crystallite size was lied in nano regime ranging from 21.8 to 36.5 nm. The surface chemical composition of the Mn0.5Zn0.5-xMgxFe2O4 NPs was investigated via XPS analysis. Mossbauer spectra showed that the peaks were shifted to higher values of the maximum magnetic field as the Mg content increased, indicating that the crystallinity is enhanced while the crystal size is decreased. Also, various parameters such as the photocatalyst dose, dyes concentration, pH, point of zero charge, and the metals leaching were studied. The point of zero charge (PZC) has found at pH = 2.38. The Mn0.5Zn0.125Mg0.375Fe2O4 NPs showed an excellent UV-assisted photocatalytic activity against Chloramine T (90 % removal efficiency) and Rhodamine B (95 % removal efficiency) after 80 min as compared to pure Mn0.5Zn0.5Fe2O4 ferrite NPs. Besides, it a recyclable catalyst at least four times with a negligible reduction of photocatalytic activity with slight elements leaching. Furthermore, the Mn0.5Zn0.25Mg0.25Fe2O4 NPs showed a high antimicrobial activity towards pathogenic bacteria and yeats.

Use of Magnetic Activated Carbon in a Solid Phase Extraction Procedure for Analysis of 2,4-dichlorophenol in Water Samples

In the present study, a composite was synthesized by the impregnation of activated carbon with magnetite (Fe3O4) using a simple co-precipitation method. Several characterizations were performed, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), point of zero charge (PZC), specific surface area, and Fourier transform infrared spectroscopy (FTIR). The magnetic activated carbon composite (MAC) was used as a new adsorbent for magnetic solid phase extraction (MSPE) of 2,4-dichlorophenol (2,4-DCP) in water samples. The main experimental parameters, such as adsorbent mass, pH, adsorbent/adsorbent contact time, volume and type of desorbent, sample volume, and desorption time were optimized. The method showed linearity in the investigated concentration range of 1 μg mL−1–6 μg mL−1 (R2 = 0.999). The limit of detection (LOD) and the limit of quantification (LOQ) were 0.293 μg mL−1 and 0.890 μg mL−1, respectively. The recoveries for the water samples ranged from 50.0% to 55.0% and the relative standard deviation (RSD) was less than 4.8%. The CAM presented application to MSPE and the magnetic properties inserted in the activated carbon (AC) contributed for the fast and easy removal of the adsorbent from the reaction medium. Thus, the proposed method proved to be easy, efficient, and environmentally friendly due to low solvent consumption.

Synthesis of Rice Husk-Derived Magnetic Biochar Through Liquefaction to Adsorb Anionic and Cationic Dyes from Aqueous Solutions

Rice husk-mediated magnetic biochar (RH-MBC) was manufactured in the present study by liquefaction method. It is applied on the anionic and cationic dyes to investigate their dye adsorption capacity from aqueous solutions. Characterization of the prepared materials has been conducted by the Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscope, energy-dispersive X-ray, transmission electron microscopy, Brunauer–Emmett–Teller, vibrating sample magnetometer and point of zero charge (PZC) analysis. From the analyses, it is revealed that the manufactured RH-MBC is super-magnetic and more porous with higher surface area compared with its parent materials. After investigating the adsorption data with different adsorption isotherm and kinetic models, the data were best-fitted with Freundlich model and pseudo-second-order model. The present material shows higher adsorption capacity for representative cationic dye CV (80.04 mg/g) rather than the anionic dye EBT (5.09 mg/g). From the FTIR, XRD, PZC and isotherm studies, it is revealed that the dyes adsorption onto the RH-MBC mainly happened due to the presence of the functional groups like C–O, Fe3O4, –OH, C=C and C–O. It is concluded that the novel functionalized RH-MBC is an approach to use the waste material (rice husk) to use for wastewater treatment and highly efficient for cationic dyes adsorption. Additionally, due to its super-magnetic properties, it is easily separable by using external magnetic field.

Stability Analysis of GMZ Bentonite Colloids: Aggregation Mechanism Transition and the Edge Effect in Strongly Alkaline Conditions

In this study, the basic physicochemical properties (composition, morphology and surface charge) of the colloids obtained from Gaomiaozi (GMZ) bentonite were analyzed and photon correlation spectroscopy (PCS) tests were conducted for looking into the effects of ionic strength and pH on the stability. The results showed that the bentonite colloids were composed primarily of montmorillonite and cristobalite, and remained stable up to at least 8 months in pure water system, and its self-coagulation was negligible. The titration curves of the bentonite colloids showed a typical titration shape of montmorillonite clay, while a common intersection at the point of zero charge (PZC) around 9.5 and a slightly higher net proton sorption capacity compared with bulk form of GMZ bentonite reported in the literature were observed. The stability was strongly PZC dependent, around which the critical coagulation concentration (CCC) value rose rapidly with increasing pH stemming from the transition of different aggregation mechanisms. Further, a more important effect of the edge charge in strongly alkaline conditions was found to exist. This work can be helpful for better understanding the stability characterization of layered clay colloids and provides a valuable reference for safety assessments of the deep geological disposal repository for high-level radioactive wastes.

Removal of harmful algal blooms in freshwater by buoyant-bead flotation using chitosan-coated fly ash cenospheres.

Harmful algal blooms (HABs) are a growing problem worldwide, damaging human and ecosystem health. In this study, a novel buoyant-bead flotation (BBF) method using chitosan-coated fly ash cenospheres (CFACs) was developed to remove HABs in freshwater. To achieve a high removal efficiency of harmful algae (Chlorella vulgaris, Scenedesmus quadricauda, and Microcystis aeruginosa), this study investigated the effects of chitosan/fly ash ratios in CFAC composite, CFAC concentration, flotation time, and pH values on the microalgae removal. The optimized ratio of CFACs is 0.1:12, and the optimized CFAC concentration is 0.3-0.7gL-1. However, the lower or higher ratios (0.1:4, 0.1:8, 0.1:16) result in microalgae reaching a zero-point charge too late or early, which failed to effectively remove HABs with an appropriate coal fly ash dosage. An optimized removal efficiency of 98.50% for Microcystis aeruginosa was reached at pH of 6.0. The optimized efficiency of Scenedesmus quadricauda and Chlorella vulgaris was 99.37% and 91.63%, respectively, at pH of 8.0. At neutral pH conditions, the surface charge of microalgae cells and CFACs are different, promoting aggregate formation. When CFACs were used to remove microalgae, aggregate size significantly influenced removal efficiency. Meanwhile, at the optimized pH and concentration, the removal efficiency of all three algal species exceeded 90.00% in 5min. The study highlights an efficient and inexpensive method for removing HABs and obtains the optimized operational conditions.

Bimetallic Pd-M (M = Pt, Ni, Cu, Co) nanoparticles catalysts with strong electrostatic metal-support interaction for hydrogenation of toluene and benzene

Herein, we reported an effective method to synthesis a series of supported bimetallic Pd-M/SiO2 (M = Pt, Ni, Cu, Co) catalysts with highly exposed and well-alloyed nanoparticles via simultaneous strong electrostatic adsorption (co-SEA), which controlled metal precursors strongly anchored onto the oppositely charged support (SiO2) by changing the pH relative to the surface point of zero charge (PZC). The toluene and benzene hydrogenation were used as probe reactions to evaluate the catalytic hydrogenation activity performance of the Pd-M/SiO2 catalysts. Compared to the catalysts synthesized by the common technique simultaneous dry impregnation (co-DI), the co-SEA Pd-Ni/SiO2 catalyst exhibited the highest turnover frequencies (TOFs) of 3.7 s−1 for benzene hydrogenation and 3.2 s−1 for toluene hydrogenation. This was attributed to the large amount of electron-deficient Pdδ+ sites on the surface of SEA Pd-M/SiO2 that easily for electron-rich benzene and toluene to adsorb. Besides, the co-SEA catalysts produced well stability and reusability without significant decrease in the catalytic activity after six runs.

Removal of cationic dye from aqueous solution using Moroccan pozzolana as adsorbent: Isotherms, kinetic studies, and application on real textile wastewater treatment

Beside others, textile industries are the major sources of discharging huge amount of highly colored wastewater. The objective of this work was to study the adsorption of methylene blue (MB), from its aqueous solution on Moroccan pozzolana. Adsorption kinetics and isotherms of MB have been experimentally studied. The support (adsorbent) was characterized by, FTIR, SEM, X-ray energy dispersive spectroscopy (EDS), X-Ray fluorescence, and its Point of Zero Charge (pHPZC) was determined. The adsorption data of MB on pozzolana was analyzed using Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models. Based on the data fitting and comparison of the correlation coefficient (R2), it is inferred that Langmuir isotherm is most closely followed with a maximum adsorption capacity of 43.86 mg g−1. The kinetic data are well described by the pseudo-second order kinetic model with a R2 value of about 0.9997. Finally, the process is used to treat the textile wastewater that mainly contains methylene blue. The Pozzolana has shown good efficiency in the treatment of real textile wastewater.

The Effectiveness Adsorption of Au(III) and Cu(II) Ion by Mangosteen Rind (<i>Garcinia mangostana </i>L.) Using Point of Zero Charge Calculation

Adsorption of Au(III) and Cu(II) by mangosteen rind adsorbent had been carried out. Mangosteen rind has several functional groups including –OH phenolics, ‒C=C‒ aromatics, and ethers. Dried mangosteen rind which was obtained from maceration was used to determine Point of Zero Charge (PZC). The most effective pH adsorption was determined by mixing adsorbent with Au(III) or Cu(II) solutions with various pH. The adsorption capacity was affected by the interaction between adsorbent and adsorbate. The solid adsorbent before and after interaction was characterized by FTIR, XRD, and microphotography. The PZC pH value of adsorbent was 3.7 while the optimum pH for Au(III) and Cu(II) were at pH 2 and pH 5, respectively. The adsorption capacity (qmax) value was 333.33 mg/g by following the Langmuir isotherm equation. The crystalline structure of adsorbent was analyzed using XRD and gave 4 peaks characteristics of gold metal on 2ϴ = 38º, 44º, 64º, and 77º after adsorption which indicated the reduction of Au(III) ions into Au(0).

Adsorptive removal of acrylic acid from the aqueous environment using raw and chemically modified alumina: Batch adsorption, kinetic, equilibrium and thermodynamic studies

Herein, raw alumina was chemically modified using strong acid (HCl) and base (NaOH) to constitute alumina adsorbents, which were applied for the removal of an emerging pollutant, acrylic acid from the aqueous environment. The as-synthesized alumina samples were characterized using FT-IR, SEM, EDX, and surface area analyzer. Characterization results revealed that the chemical modification of alumina did not affect its chemical nature. SEM images demonstrated the porous nature of alumina with irregular shape and rough texture. EDX data shows the elemental composition as Al and O in raw alumina while Cl and Na were found as additional elements in acid (HCl) alumina and base (NaOH) modified alumina, respectively. BET specific surface area of alumina samples was in the range from 155.63–158.36 m2/g. The point of zero charges (PZC) was also determined and found to be 5.9, 6.4 and 9.0 for raw, acid (HCl) and base (NaOH) modified alumina, respectively. In the adsorption study, pH 4.5, 25 °C and 72 and 24 h using the raw and chemically modified alumina, respectively, were found to be the best experimental conditions using 0.1 mol/L acrylic acid solution and 1.0 g alumina. During the consecutive desorption experiments, 86.9 ± 2.5–95.5 ± 3.8 % acrylic acid was desorbed at pH 13. The data follows the pseudo-second-order kinetic and Freundlich adsorption models with 4080–4330 μmol/g adsorption capacity. Moreover, the adsorption process was non-spontaneous and exothermic with the lowering of the randomness of the system at the solid-solution boundary. In conclusion, the high uptake capacity and recyclable nature of the alumina adsorbents render them as promising candidates for the remediation of wastewater and industrial effluents containing such toxic pollutants.

Temperature and pH responsive behavior of antifouling zwitterionic mesoporous silica nanoparticles

Zwitterionic brush grafting is considered a serious strategy for surface modification on mesoporous silica nanoparticles (MSN) and a prominent alternative to polyethylene glycol films for antifouling applications. In this study, the solution behavior of poly(sulfobetaine methacrylate) (pSBMA) polymer brushes grafted on MSN (95 ± 15 nm particle diameter, 2.8 nm pore size) was evaluated. The layers increased their hydrodynamic diameter (dH) with increasing temperature, indicating a conformational change from a surface-collapsed state to a fully solvated brush. This development was marked by a transition temperature, related to the molecular weight and the theoretical length of the polymer chains. Variation of dH with pH values was studied and a zwitterionic range of 5–9 was established where the electric charges in the molecule were balanced. Zeta potential (ZP) values for all pSBMA-MSN products were also measured. A decreasing trend of ZP with pH and an isoelectric point around 5.5–6.5 was obtained for all dispersions. Furthermore, the influence of temperature was analyzed on ZP and a directly proportional correlation was found, with increasing rates of 0.50–0.87%/°C. Finally, ZP variation with electrolyte concentration was determined and a range of 40–60mM of NaCl concentration was established to reach an almost zero-charge point for all nanoparticles. It was demonstrated that the solution response of pSBMA-MSN can be modulated by temperature, pH, and ionic concentration of the media. These behaviors could be used as controlled release mechanisms for the application of pSBMA-MSN as carriers in biomedicine and nanophamaceutical fields in the future.

Citric acid modified granular activated carbon for enhanced defluoridation

Excess fluoride (F−, >1.5 mg F−/L) in drinking water affects >260 million people across the globe and leads to dental and skeletal fluorosis. In this study, commercially available granular activated carbon (GAC) was modified with 0.3 M citric acid to get citric acid modified GAC (CAGAC). Over 70% of fluoride was removed in the first 60 min by CAGAC, whereas unmodified GAC removed only 30%. There were negligible interferences by co-existing ions (NO3−, Cl−, HCO3−, SO42−, PO43−) and organic matters. Maximum adsorption capacity of CAGAC was two times (1.65 mg/g) that of unmodified GAC (0.88 mg/g). Dubinin-Radushkevich (D-R) isotherm described the experimental data well indicating that ion exchange was involved in fluoride removal. CAGAC worked effectively over a wide range of pH (2–10) even though the point-of-zero-charge (PZC) was 4.89, and so the removal was not controlled by electrostatic interaction alone; surface adsorption and intra-particle diffusion were the rate-determining processes.

Synthesis and characterization of ZnO nanoparticles via zeolitic imidazolate framework-8 and its application for removal of dyes

Zinc oxide (ZnO) nanoparticles were obtained via calcination of zeolitic imidazolate framework-8 (ZIF-8). The activities of prepared ZnO nanoparticles at different temperature 450, 550, and 650 °C were investigated for the adsorption of acid red 57 (AR57) and remazole red (RR) dye. The synthesized ZnO nanoparticles were characterized by different spectroscopic studies such as FTIR, X-ray diffraction, energy-dispersive X-ray spectroscopy, N2 adsorption–desorption and pH titration for determination of Zero-point charge (pHZPC). The mechanism of adsorption behavior of AR57 and RR are studied with respect to temperature, pH and concentration. Experimental data indicated that the adsorption capacity of ZnO for AR57 and RR was higher in acidic rather than in basic solutions. The activation energy of adsorption was also evaluated for the adsorption of AR57 and RR onto ZnO nanoparticles. Langmuir and Freundlich adsorption models were also applied to describe the equilibrium isotherms and the isotherm constants. The pseudo-first-order and pseudo-second-order model equations were used to analyze the kinetics of the adsorption process. The adsorption efficiency of ZnO nanoparticles was found in the order: 450 > 550 > 650 °C. The activation energy, enthalpy, change of free energy and entropy of adsorption were also evaluated for the adsorption of AR57 and RR onto ZnO nanoparticles. The thermodynamics of the adsorption indicated spontaneous and exothermic nature of the process.

Catalytic activity of Pt/graphene prepared by strong electrostatic adsorption technique for proton exchange membrane fuel cells

In the proton exchange membrane (PEM) fuel cell development, the catalytic activity requires the smaller particle size, the better metal dispersion, the higher conductivity and the longer durability. With these, platinum on graphene was synthesized using the strong electrostatic adsorption (SEA) technique. The pH shifts of graphene was evaluated and the point of zero charge (PZC) was obtained at pH about 5.2. This was a mid-low PZC, where the positive charge of Pt (i.e, platinum tetraamine, [NH3]4Pt2+or PTA) was chosen as the metal precursor. The adsorption of PTA precursor on graphene was carried out at pH of 12 for one hour at room temperature. PTA on graphene was reduced in hydrogen environment, and transferred to Pt metal particle. The adsorption and reduction steps were repeat until the Pt metals percentage closed to 20%wt Pt/C (i.e, 19.3 % wt. for this work). The prepared Pt/graphene catalyst shows the smaller particle size that average particle size as 2.4 nm and highly better dispersion than the Pt/C-commercial. The Pt metal dispersion on the graphene support were inspected by transmission electron microscopy (TEM). The crystal structures and crystalline size were investigated by X-ray diffraction (XRD). Moreover, the electrochemical properties were tested using cyclic voltammetry (CV) and the accelerated durability test (ADT) was also carried out after 4000 cycles of reduction and oxidation reaction. Finally, the results were compared with the 20% wt. Pt/C-commercial catalysts. It was observed that the oxidation reduction reaction (ORR) activity in terms of mass activity (MA) and specific activity (SA) were better than Pt/C-commercial.

Interfacial electrochemical properties of natural Moroccan Ghassoul (stevensite) clay in aqueous suspension

A raw Moroccan clay locally named “Ghassoul” (Gh) was characterized using several techniques such as Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), Brunauer, Emmett and Teller method (BET), Scanning Electron Microscopy (SEM) and simultaneous Thermo-Gravimetric and Differential Thermal Analysis (TGA/DTA). These techniques indicate that the Gh consists essentially of steveniste, calcite, dolomite and quartz. The study of the interfacial electrochemical properties of Gh in different solutions of electrolyte salts (NaCl, CsCl, NaF, NaBr and LiCl) was carried out using the potentiometric and conductometric titrations It was shown that the Gh particles were stable in aqueous phase within the pH range (3–12) and the point of zero charge (PZC) was located at pH = 10.7. The adsorption sequence, carried out at various ionic strengths, showed that the adsorption mechanism onto the Gh particles is both electrostatic and specific at pH below the pHpzc, while at a pH range greater than the pHpzc the mechanism is electrostatic in nature. The total number of surface sites, determined using the graphical extrapolation method, was 11OH/nm2. Ionization constants (pKint+ and pKint−) in the presence of various electrolytes have also been determined and their values are 10.08 and 12.38, respectively.

Effect of biochar modified with magnetite nanoparticles and HNO3 for efficient removal of Cr(VI) from contaminated water: A batch and column scale study

Chromium (Cr) poses serious consequences on human and animal health due to its potential carcinogenicity. The present study aims at preparing a novel biochar derived from Chenopodium quinoa crop residues (QBC), its activation with magnetite nanoparticles (QBC/MNPs) and strong acid HNO3 (QBC/Acid) to evaluate their batch and column scale potential to remove Cr (VI) from polluted water. The QBC, QBC/MNPs and QBC/Acid were characterized with SEM, FTIR, EDX, XRD as well as point of zero charge (PZC) to get an insight into their adsorption mechanism. The impact of different process parameters including dose of the adsorbent (1–4 g/L), contact time (0–180 min), initial concentration of Cr (25–200 mg/L) as well as solution pH (2–8) was evaluated on the Cr (VI) removal from contaminated water. The results revealed that QBC/MNPs proved more effective (73.35–93.62-%) for the Cr (VI) removal with 77.35 mg/g adsorption capacity as compared with QBC/Acid (55.85–79.8%) and QBC (48.85–75.28-%) when Cr concentration was changed from 200 to 25 mg/L. The isothermal experimental results follow the Freundlich adsorption model rather than Langmuir, Temkin and Dubinin-Radushkevich adsorption isotherm models. While kinetic adsorption results were well demonstrated by pseudo second order kinetic model. Column scale experiments conducted at steady state exhibited excellent retention of Cr (VI) by QBC, QBC/MNPs and QBC/Acid at 50 and 100 mg Cr/L. The results showed that this novel biochar (QBC) and its modified forms (QBC/Acid and QBC/MNPs) are applicable with excellent reusability and stability under acidic conditions for the practical treatment of Cr (VI) contaminated water.

Ion-Exchanged ZIF-67 Synthesized by One-Step Method for Enhancement of CO2 Adsorption

Li+- and Na+-exchanged ZIF-67 was synthesized by a new one-step method of ion as-exchange technique and tested as CO2 adsorbents. As a comparison, the standard ion-exchange procedure was also carried out. The powder X-ray diffraction (XRD), scanning electronic microscope (SEM), particle size analyzer (PSD), and thermal gravimetry analysis (TGA) were used to investigate the effect of ion-exchange techniques on the structure of the materials. CO2 uptake of ZIF-67 ion exchanged by one-step method is much higher than that by the standard ion-exchange procedure. All of the adsorption isotherms show linear patterns with stable adsorption rate from 0 bar to 1 bar, which reveals the materials could get excellent adsorption performance at higher pressure range (>1 bar). Elemental analysis, N2 physical adsorption, and the point of zero charge (PZC) were carried out to confirm the adsorption mechanism. van der Waals interaction determined by the surface area and coordination interaction resulting from electrostatic interaction work in synergy to enhance CO2 adsorption performance of ZIF-67 ion exchanged by the one-step method.