Initial Chromium Concentration Research Articles

Chitosan/Graphene oxide/SiO2 Nanoadsorbents for the Removal of Cr(VI) from Wastewaters

The swift industrialization and urbanisation have led to the discharge of significant amounts of hazardous heavy metals into water environments. Heavy metal pollution is currently one of the most significant environmental challenges being addressed, attracting researchers due to its biotoxicity, and non-biodegradability even at minimal concentrations [1]. Chromium (Cr) is among the most prevalent heavy metal contaminants. Its oxidation state, Cr(VI), harms the environment yet has catastrophic consequences for human health [2]. It is removed by physical and chemical procedures such as ion exchange, chemical precipitation and electrochemical treatment. Yet, most of these procedures have downsides, such as the formation of hazardous sludge, causing disposal issues and the need for costly tools and monitoring systems [3]. Adsorption is regarded an appealing and favourable technology because to its ease of design, simplicity, and high efficiency. Carbon-based nanomaterials have been investigated as superior adsorbents in aqueous solutions for the separation of organic and inorganic contaminants. The current study recommends the usage of adsorbents based on graphene oxide (GO). GO is an oxygen-rich material that is produced during the oxidation of graphite. It features hydrophobic areas due to aromatic groups in the nanosheets' centres, along with a large number of hydrophilic functional groups such as hydroxy, aldehyde, epoxy, and carboxyl groups [4]. The latter allow GO to swell and perform electrostatic functions. Chitosan (Cs) is a great adsorbent since it is inexpensive, is biocompatible, and causes no secondary pollution. Its molecular chains include -NH2 and -OH groups, which can interact with heavy metal ions and give significant adsorption capacity [5]. Silicon dioxide (SiO2) nanoparticles with graphene oxide have better physical and chemical characteristics than graphene oxide-like surface area. Similar research has revealed that the presence of SiO2 increases the adsorbent's adsorption capacity for Cr(VI) [6]. The effect of the pH value, contact time and initial chromium concentration was examined in order to determine the feasibility of Cs/GO@SiO2. Its structure and the morphology were studied in detail by the application of BET, XRD, FTIR and SEM techniques. According to the results, the modification of Cs with GO@SiO2 enhanced the percentage removal of chromium ions, especially, in acidic conditions by using 0.5 g/L of the adsorbent. Experimental data of equilibrium were used to calculate adsorption isotherms. According to thermodynamics the spontaneous nature of their adsorption was confirmed. Overall, the results indicate that Cs/GO@SiO2 can be effectively employed for removal of chromium from aqueous solutions.

Hexavalent chromium adsorption from aqueous solution utilizing activated carbon developed from Rumex abyssinicus

The indiscriminate release of chromium-saturated effluent into water bodies has raised concerns regarding its effect on human health and environmental ecology. Therefore, this research aimed to remove hexavalent chromium from an aqueous solution utilizing activated carbon developed from Rumex abyssinicus. The adsorbent was prepared through chemical impregnation with H3PO4 and then thermally activated at 500 °C for 2 h. The optimization of the adsorption experiments was performed using the Box‒Behnken approach of response surface methodology. The characterization of the prepared activated carbon revealed good quality in terms of its amorphous structure, maximum specific surface area of 1722.9 m2/g and porous surface. Furthermore, the optimization results showed that a maximum removal efficiency of 95.97 % was attained at an optimum working pH of 3, a contact time of 60 min, an initial chromium concentration of 70 mg/L and an adsorbent dosage of 0.6 mg/100 mL. The Langmuir isotherm model was found to have the best fit with the experimental data. Moreover, the kinetics study revealed that a pseudo-second-order model fit the data best, indicating the occurrence of chemisorption. Overall, this study suggested that Rumex abyssinicus could be an effective adsorbent for removing hexavalent chromium from aqueous solutions.

Artificial neural network approach to model Cr(III) and Cr(VI) adsorption by NCS, ACS and BCS

Adsorption properties of Cr(III) and Cr(VI) on natural (NCS), acid-activated (ACS) and base-activated (BCS) cherry stalks (CS) in Isparta were investigated in aqueous solutions. Batch adsorption studies had been completed with different initial chromium concentrations, pH, temperature, time and biosorbent dosage. Adsorption rapidly approached an equilibrium state between 10 and 60 min. The results displayed that the adsorption system was suitable for pseudo-second-order kinetics. Equilibrium isotherms (Langmuir, Freundlich and Dubinin–Radushkevich) were measured experimentally. The retention characteristics of Cr(III) onto NCS, ACS and BCS and Cr(VI) onto ACS were represented by Langmuir adsorption isotherms, while Cr(VI) ions onto NCS and BCS were compatible with Freundlich adsorption isotherms. The adsorption process was endothermic accompanied by a decrease in entropy and Gibbs energy. An artificial neural network (ANN) model was improved to estimate the efficiency of Cr(III) and Cr(VI) ion’s adsorption. The ANN model can predict the behaviour of the Cr(III) and Cr(VI) ion's adsorption under different circumstances. The results have shown that NCS, ACS and BCS biosorbents open up new possibilities and potential commercial uses in the cherry stalks.

Taguchi method for optimization of Cr(VI) removal, isotherm, kinetic and thermodynamic studies

In this study, Taguchi optimization method was applied to determine the optimum operating conditions for batch adsorption of Cr(VI) from aqueous solution. Initial pH of solution, adsorbent dose, initial hexavalent chromium concentration, contact time and adsorbent type were selected as the variables, and the removal efficiency of Cr(VI) was chosen for the designated response. L18(35) orthogonal array, signal-to-noise (S/N) ratio and analysis of variance statistical procedures were applied to identify the effect of each operating parameter on the removal of Cr(VI) from aqueous solution. The signal-to-noise (S/N) ratio results showed that the optimal combination for Cr(VI) removal was at pH 1.0, adsorbent dose of 3.6 g.L−1, Cr(VI) concentration of 30 mg.L−1, contact time of 95 min and olive leaves as adsorbent type. A removal of 95.09% was obtained at these optimum conditions. The analysis of variance of the data revealed that initial pH of solution was the most dominant parameter affecting Cr(VI) removal efficiency, followed by adsorbent type, adsorbent dose, contact time and initial metal concentration. Under optimal conditions, adsorption kinetic of Cr(VI) was studied and modeled using the pseudo first-order, pseudo-second-order and intraparticle diffusion models. It was found that the pseudo-second-order model fitted the adsorption data most with the highest determination coefficient (R2 = 0.996). Freundlich isotherm model, with regression coefficient R2 of 0.953, fit well with the equilibrium isotherm data. The Langmuir maximum adsorption capacity was found to be 62.5 mg.g−1. The experimental values of ΔH°, ΔG° and ΔS° revealed that the adsorption process was spontaneous and endothermic.

Chromium adsorption using powdered leaves of Prosopis cineraria: Kinetic, isotherm, and optimization by response surface methodology

In this study, the effectiveness of Prosopis cineraria leaves powder in removing chromium from an aqueous solution was examined. The test was done in batch mode and the effect of Prosopis cineraria doses (1–5 g/L), initial pH (1.5–3.5), initial concentrations of chromium (10–50 mg/L), and contact times (15–75 min) on the biosorptioon process was examined. The results of response surface methodology indicated that under the best operating conditions with Prosopis cineraria dose of 3.98 g/L, initial chromium concentration of 25.41 mg/L, contact time of 59.82 min and pH of 2.02, chromium removal efficiency was selected as a maximum value of 89.65%. The adsorption aligns with the Langmuir isotherm and pseudo-first-order kinetic models. The maximum adsorption capacity for chromium was determined to be 55.55 mg/g, indicating the high efficacy of Prosopis cineraria in removing chromium ions. The findings suggest that Prosopis cineraria leaves powder could be a cost effective alternative to more expensive heavy metal adsorbents from aqueous solution, but notes more research is needed on the efficiency of Prosopis cineraria for industrial wastewater. Future studies should focus on SEM, XRD and FTIR analysis to enhance understanding of the adsorption mechanisms and potential applications for chromium removal.

Adsorption removal of copper (II) and chromium (VI) from wastewater by Fe3O4-loaded granular activated carbon

Abstract Combining with the characteristics of Fe3O4 and activated carbon, magnetic granular activated carbon (GAC–Fe3O4) was prepared by chemical coprecipitation. With GAC–Fe3O4 as the adsorbent, the effects of GAC–Fe3O4 dosage, the initial pH of wastewater temperature, and the initial concentration of copper (II) and chromium (Ⅵ) on the removal performance were explored. The adsorption process of copper (II) and chromium (VI) on magnetic GAC was studied using adsorption kinetics, adsorption isotherms, scanning electron microscopy, and infrared spectroscopy. The experimental results indicate that among these influencing factors, the pH value of wastewater plays a vital role in the removal efficiency. When the pH value was 6 and 2, the initial concentration of copper (II) and chromium (VI) ions was 5 ppm, the optimum removal efficiencies of copper (II) and chromium (VI) were 99.98 and 96.39%, respectively. As to the adsorption mechanism of GAC–Fe3O4, the adsorption of copper (II) and chromium (VI) in wastewater was more consistent with the Langmuir model. The adsorption process in this study can be well explained by the pseudo-second-order kinetic model.

Removal of chromium from tannery industry wastewater using iron-based electrocoagulation process: experimental; kinetics; isotherm and economical studies

Chromium is a hazardous compound from industrial processes, known for its toxicity, mutagenicity, teratogenicity, and carcinogenicity. Chemical methods are efficient but cost-effective alternatives with reduced sludge are sought. Electro-coagulation, utilizing low-cost iron plate electrodes, was explored for factual tannery wastewater treatment in this manuscript. Operating parameters such as initial chromium concentration, voltage, electrode number, operating time, agitation speed and current density has been studied to evaluate the treatment effeciency. Under optimal conditions (15 V, 0.4 mA/cm2, 200 rpm, 330 ppm chromium, 8 iron electrodes with a total surface area of 0.1188 m2, 3 h), chromium elimination was 98.76%. Iron anode consumption, power use, and operating cost were 0.99 gm/L, 0.0143 kW-h/L, and 160 EGP/kg of chromium eliminated, respectively. Kinetics studies were pursued first-order reaction (97.99% correlation), and Langmuir isotherms exhibited strong conformity (Langmuir R2: 99.99%). A predictive correlation for chromium elimination (R2: 97.97%) was developed via statistical regression. At HARBY TANNERY factory in Egypt, industrial sewage treatment achieved a final chromium disposal rate of 98.8% under optimized conditions.

Amino-modified hemp stem for high-capacity adsorption of Cr(VI) from aqueous solution

Two novel adsorbents, triethylenetetramine-grafted hemp stems (HS-TETA) and choline chloride-grafted hemp stems (HS-CL), were prepared by using epichlorohydrin as etherifying agent. The obtained adsorbents were comprehensively characterized, and the adsorption capacity for hexavalent chromium (Cr(VI)) was evaluated under various single-factor conditions, including adsorbent dosage, contact time, solution pH, initial hexavalent chromium concentration, and temperature. HS-TETA and HS-CL exhibit excellent adsorption performance, with maximum adsorption capacities of 396.88 and 335.04 mg/g, respectively, outperforming previous relevant studies. The adsorption behavior of Cr(VI) by HS-TETA and HS-CL was investigated using adsorption kinetics, adsorption isotherms, and adsorption thermodynamics. The adsorption process follows the pseudo-second-order kinetic model and the Langmuir isotherm model, suggesting a monolayer adsorption process with chemical adsorption. Thermodynamic analysis reveals that the adsorption of Cr(VI) on two adsorbents is spontaneous and exothermic. Combined with the characterization, it can be speculated that the adsorption of Cr(VI) on two adsorbents involves electrostatic effects, reduction, and complexation processes. HS-TETA and HS-CL exhibit good recyclability. After 5 cycles, HS-TETA and HS-CL maintain over 50% and 85% of their initial adsorption capacity, respectively. The cycling performance of HS-CL containing quaternary ammonium and amine groups is significantly superior to that of HS-TETA containing only an amine group, indicating that the introduction of the quaternary ammonium group enhances the cycling performance of the adsorbent. HS-TETA and HS-CL, as cost-effective and efficient adsorbents, offer a promising solution for the treatment of Cr(VI)-contaminated wastewater and facilitate the recycling of agricultural waste.

Advancing the development of nanocomposite adsorbent through zinc-doped nickel ferrite-pinecone biochar for removal of chromium (VI) from wastewater

Leather and textile industrial effluents are the main disseminating routes for chromium contamination of water bodies, causing adverse impacts on public and environmental health. The attempt to remediate chromium through conventional wastewater treatment methods is inefficient. Therefore, this study aims to synthesize zinc-doped nickel ferrite pinecone biochar (Zn-NiF@PBC) nanocomposite for the removal of chromium from wastewater systems. The Zn-NiF@PBC nanocomposite was synthesized via the co-precipitation method. The properties of zinc-doped nickel ferrite (Zn-NiF) were effectively modified by blending with biochar at 1, 5, 10, and 15 % (w/w) which was successfully embedded with Zn-Ni ferrite nanoparticles. This was characterized and confirmed by typical adsorbent properties such as a high surface area of 104 m2/g, conducive pore volume of 0.117 cm3/g and pore size of 3.41 nm (BET), interactive multi-functional groups (FTIR), surface charge determination (pHpzc,), crystalline structure (XRD) and very rough surface morphology (SEM). The maximum chromium adsorption was found to be 95 % at the specific experimental condition of pH 3, adsorbent dose 1 g/50 mL, contact time 120 min, and initial chromium concentration 100 mg/L. The adsorption experimental data was best fitted with the Langmuir isotherm at R2 0.98 indicating the adsorption process was homogeneous and monolayer whereas the kinetics adsorption was resembling the second-order kinetic at R2 0.99. Moreover, the adsorption thermodynamics was spontaneous, endothermic, and increased the change in entropy. Finally, the regeneration of Zn-NiF@PBC was found to be effective up to five 5 cycles but gradually degrading in terms of removal efficiency after 3 cycles. In general, Zn-NiF@PBC can remediate chromium from wastewater with huge potential for scale-up and extend to other pollutants clear-up.

Cr(VI) removal and mechanism from simulated polluted groundwater by Klebsiella variicola H12-CMC-FeS@biochar assisted permeable reactive barrier

Permeable reactive barrier(PRB) is an attractive technique for in situ polluted groundwater remediation. Klebsiella variicola H12-Carboxymethylcellulose -FeS@biochar (K.variicola H12-CMC-FeS@biochar) was used as filling medium in PRB to remove chromium contamination from simulated groundwater. The results showed that the chromium removal efficiency was 94 %, which was more effective than k. variicola H12 or biochar respectively and the optimal solid-liquid ratio was 30:1. Ionic strength and initial chromium concentration in groundwater have greater influence on the treatment effect. Scanning electron microscopy(SEM) and fluorescence microscopy showed that biofilm covered on the surface of the material. X-ray Photoelectron Spectroscopy(XPS) indicated that most of hexavalent chromium(Cr(VI)) and trivalent chromium(Cr(III)) were adsorbed by k. variicola H12-CMC-FeS@biochar. Cr(III) originated from the reduction of chromium by K. variicola. Furthermore, quantitative real-time polymerase chain reaction(qPCR) results showed that the expression level of ChrA, ChrB and ChrR genes increased, which contributed to relieve cytotoxicity. These changes improved the resistance of k. variicola H12 to Cr(VI), promoting Cr(VI) reduction. In summary, biofilm adsorption and microbe reduction were the two primary ways to enhance the chromium removal efficiency. It provided a new method for treating in-situ groundwater pollution by PRB technology using biochemical materials as mediums.

Obtaining and study of physical-chemical properties of porous materials based on kaolin

The object of research is kaolin from the Hlukhovetsky deposit (Ukraine). On its basis, granulated sorbent materials were obtained with the addition of various amounts of cellulose as a pore former. After forming the samples, they were dried and fired at a temperature of 800 °C. The obtained granules with a size of 8–9 mm were modified with zero-valent iron. The physicochemical, including sorption properties of granular composites were studied. Using scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), the morphology of the obtained samples was investigated and the presence of zero-valent iron particles on the surface and in the pores of the sorbents was confirmed. Based on desorption experiments, it was determined by chemical analysis that the Fe0 content in modified samples with increased pore former content increases from 0.01 g/g of granules for a sample containing 1% cellulose to 0.016 g/g for a carrier with 3 % pore former. The specific surface area and pore volume of the samples were determined by the method of low-temperature adsorption-desorption of nitrogen. Thus, with an increase in the content of the pore former in the ceramic mass, the specific surface of both unmodified and modified samples slightly decreases. Thus, with a cellulose content of 1 %, it is 20 m2/g and 17 m2/g, respectively. When the pore former is increased to 3%, these values are 15 m2/g and 12 m2/g. After applying a layer of zero-valent iron on porous granules, the volume of pores decreases, which is due to the formation of agglomerates of iron particles during synthesis. The study of the sorption capacity of the obtained sorbents with respect to Cr(VI) from model solutions containing a mixture of metal cations (copper, cadmium, cobalt, zinc) showed that granular materials exhibit sorption capacity for metal anions, even in the presence of cations. The amount of chromium sorption naturally increases for modified samples with an increase in the cellulose content in them. However, for model solutions that do not additionally contain metal cations, the sorption value is somewhat higher. Thus, for a sample with a 3 % pore former content, the sorption value is 0.7 mg/g and 0.9 mg/g, respectively, at an initial chromium(VI) concentration of 10 mg/g. The obtained experimental data indicate that the obtained porous granular sorbents based on kaolin can be used in the further treatment of wastewater from electroplating enterprises, which contain a mixture of pollutants in both anionic and cationic forms.

Study of the Adsorption Efficacy of Cr(III) on a Metal Oxide-Based Material Derived from the Quartz Sand Enrichment Process

In the present study, the efficacy of chromium removal from water media was studied. For this purpose, a metal oxide based material, derived from the enrichment process of quartz coastal sand was used as possible adsorbent of chromium (III) ions. Following additional modification of the adsorbent, the effect of operational parameters including pH, contact time and Cr(III) concentration were studied according to one-factor-at-a-time procedure. Adsorption efficacy was assessed by the measurement of the remaining chromium concentration in solution, after adsorption. Atomic absorption spectroscopy technique, with flame atomization was used for the determination of chromium concentration in solution. Obtained results revealed that selected material exhibited higher adsorption efficacy in alkaline solution (pH = 6-9). The maximum removal efficacy (>93%) was achieved after 180 minutes of contact time, with an adsorbent dosage of 5 g/L and initial chromium concentration 20 mg/L. The adsorption process for Cr(III) follow the Freundlich isotherm and gives high correlation coefficient R². Calculations performed based on the Langmuir isotherm showed that the maximum adsorption efficiency of Cr³⁺ in the natural metal-oxide material has resulted 10 mg/g or 10000 μg/g. Pseudo second order reaction kinetics has provided a realistic description for removal of Cr(III) from solution with high correlation coefficient R² of (0.999). The adsorption isotherms were better described by the Freundlich equation (R² = 0.934). Adsorption of trivalent chromium ions onto selected material followed the pseudo second order model (R² = 0.996). Hence, the residual materials derived from the enrichment processes of quartz sand can be used as alternative adsorbent for the removal of trivalent chromium ions from aqueous solutions.

Preparation of Fe3O4/vine shoots derived activated carbon nanocomposite for improved removal of Cr(VI) from aqueous solutions

In this study, Fe3O4/activated carbon nanocomposite was successfully synthesized for removal of Chromium from aqueous solutions. The Fe3O4 nanoparticles were decorated on vine shoots-derived activated carbon using co-precipitation method. The atomic absorption spectrometer was used to evaluate the removal of Chromium ions by the prepared adsorbent. The effect of various parameters such as adsorbent dose, pH, contact time, reusability, electric field, and initial Chromium concentration were examined to find the optimum conditions. According to the results, the synthesized nanocomposite showed a high ability to remove Chromium at an optimized pH of 3. At optimum conditions, a high removal efficiency of 90% and an excellent adsorption capacity of 305.30 mg/g was obtained. In addition, adsorption isotherms and adsorption kinetics were studied in this research. The results showed that the data are well fitted with the Freundlich isotherm and the adsorption process is spontaneous and follows the pseudo-second-order model.

Valorization of Groundnut Shell Biomass for Biosorption of Hexavalent Chromium from Aqueous Solution

Biosorption is a cost-effective biotechnological innovation for the removal of heavy metals from aqueous solutions. There is widespread research into ways of utilizing agricultural residues to achieve zero waste. Groundnut shells are biodegradable waste available in large quantities. This study investigated the use of groundnut shells for the biosorption of chromium (VI) ions from an aqueous solution. Groundnut shells were cleaned and crushed to make fractions of particle size in the range of 90-1000 µm. The point of zero charge (pHPZC) and the distribution of oxygenated acidic and basic surface functional groups were determined. In batch experiments, the effect of acid pre-treatment, initial metal concentration, biosorbent particle size, biosorbent dosage, and contact time on biosorption was investigated. The biomass was found to have a pHPZC value of 6 and was dominated by acidic groups. The best biosorption activity was observed at 20 mg/L initial metal concentration and a biosorbent dosage of 10%. The effect of contact time was dependent on the initial chromium (VI) concentration. At 20 mg/L initial chromium (VI) concentration, the biosorption process reached equilibrium within 60 minutes whilst at high (>80 mg) chromium (VI) concentration equilibrium was not reached, even after 240 minutes. The best biosorption activity was observed with acid-treated biomass of particle size 300 µm. The adsorption fitted best with the Langmuir isotherm model and the pseudo-second-order kinetic model (R2 > 0.9982). Groundnut shell biomass has the potential for the removal of chromium (VI) ions from aqueous solutions and possibly from chromium-polluted effluents on an industrial scale.

Light intensity effect on the performance of Rhodobacter capsulatus in removal of chromium from effluent

The research aims to evaluate an unusual photosystem removing hexavalent chromium and total chromium contamination from the effluent by bioremediation (Rhodobacter capsulatus). Biomass and pigments (bacteriochlorophyll and carotenoid) production through different light intensities (dark, 800 lx, 3,200 lx, 5,670 lx, and 8,000 lx) were verified. The cultures were inoculated in 250 mL Erlenmeyer and operated under anaerobic conditions for 192 h. RCV medium with hexavalent chromium (10 mg/L, 30 mg/L, 60 mg/L, 90 mg/L, and 110 mg/L) was used. The findings show there was complete removal of hexavalent chromium. The increase in light intensity reduced the time for removal. Concerning total chromium, maximum removal occurred under 5,670 lx at low initial concentrations of hexavalent chromium of 10 mg/L (80.2 %), 30 mg/L (89.3 %), and 60 mg/L (77.0 %). Furthermore, the increase in light intensity up to 5,670 lx favored cell growth and pigment production. At 5,670 lx, there was a 230 % increase in biomass content in the culture with an initial concentration of 60 mg/L of hexavalent chromium. The final pigment contents were 2.22 mg/m3 (bacteriochlorophyll) and 1.44 mg/m3 (carotenoid).

Treatment of Tannery Effluent Using Combined Electrocoagulation and Adsorbent of Powdered Marble

This paper discusses the ability to remove chromium and COD from a real chrome tanning wastewater by use of Electrocoagulation (EC) coupled with adsorption using Powdered Marble (PM) added to a batch stirred EC cell with a pair of duralumin electrodes. The effects of current density, adsorbent dose and contact time were studied. In comparison to the conventional EC process, the coupling of electrocoagulation and adsorption using powdered marble showed that the addition of an appropriate powdered marble improved the removal of Cr(III) and COD using lower current densities and a short contact time. Nearly 99% of Cr(III) and COD were removed from tanning effluent with an initial chromium concentration of 3.21 g/L and COD of 3.75 g/L. the results obtained showed better performance using combined electrocoagulation and adsorbent of powdered marble compared to the simple EC.

CuO improved energy band of AgO/fibrous SiO2–ZrO2 for optimized simultaneous photocatalytic redox of chromium (VI) and p-cresol using response surface methodology

Ternary CuO/AgO/FSZr photocatalysts were fabricated via the hydrothermal and electrochemical methods with three different CuO loading (1, 3 and 5 wt%), indicated as 1CuO/AgO/FSZr, 3CuO/AgO/FSZr and 5CuO/AgO/FSZr. The photocatalytic reaction was tested towards simultaneous chromium (VI) photoreduction and p-cresol photooxidation and the performance in order as follow: 3CuO/AgO/FSZr > 5CuO/AgO/FSZr > 1CuO/AgO/FSZr > AgO/FSZr > FSZr. CuO/AgO/FSZr photocatalysts showed an improvement in photocatalytic activity compared to AgO/FSZr and FSZr due to the reduction potential of chromium (VI) aligned closer to the conduction band of CuO and provided abundant free active electrons (e−) and holes (h+) with efficient transportation and migration. Interestingly, the 3CuO/AgO/FSZr was established as the best photocatalyst with 98% reduction of chromium (VI) and 83% oxidation of p-cresol simultaneously, owing to its strong corporation between the metal oxides and support and higher total pore volume. The Langmuir-Hinshelwood model were employed for kinetics which followed the pseudo-first-order kinetics model well. Based on the simultaneous photocatalytic mechanism, chromium (VI) and p-cresol were directly reduced and oxidized by e− and h+, respectively. The response surface methodology (RSM) discovered that the quadratic term initial concentration of chromium (VI) is the main significant factor in photocatalytic performance. The optimum parameters for simultaneous photoredox of chromium (VI) and p-cresol predicted from RSM are 9.6 mg L−1 of chromium (VI) concentration, 9.8 mg L−1 of p-cresol concentration and 0.32 g L−1 of catalyst dosage. Under these conditions the error between the predicted and experimental values is only 3.7%. The 3CuO/AgO/FSZr sustained the photocatalytic performance after reused for five cycles and could oxidized various organic pollutants as well as reduced chromium (VI) simultaneously.

Bio-fabrication of porous magnetic Chitosan/Fe3O4 nanocomposite using Azolla pinnata for removal of chromium – Parametric effects, surface characterization and kinetics

In this research, a novel porous nanocomposite, namely Chitosan-iron-oxide @ Azolla pinnata nanocomposite, has been synthesized by co-precipitation and hydrothermal method. The effect of process parameter on adsorption process was investigated. Batch removal of chromium (Cr) was optimized with respect to solution pH, batch stirring time, sorbent dose, initial chromium concentration and temperature. The maximum removal efficiency was found to be 98.58%. The Fourier transform infrared (FTIR) spectroscopy and scanning electron microscope (SEM) analysis of the nano composite confirmed the presence of characteristic functional groups and porous structure of synthesized nanocomposite. The adsorption data fitted well with Langmuir adsorption isotherm (R2 = 0.996) confirming mono layer sorption and the maximum uptake was found to be 294.12 mg/g. The adsorption was found to follow pseudo second order model (R2 = 0.997). Thermodynamic studies revealed that adsorption is endothermic and spontaneous. Reusability studies have confirmed that removal efficiency attained was 85% after completion of five adsorption-desorption cycles. Electrostatic attraction, ion exchange, coordination bonding and reduction are the major mechanisms responsible for removal of chromium. Surface modification of Azolla pinnata with chitosan and iron oxide improved the ability of Azolla in the adsorption of chromium from aqueous media. The combined effects of facile synthesis, improved adsorption features and easier magnetic separation promotes Chitosan-iron-oxide @ Azolla pinnata nanocomposite as a novel adsorbent.

Synthesis of a first generation (G1) PPI dendrimer functionalized with 4-hydroxycoumarin effective for the removal of chromium (III) and chromium (VI) by adsorption

The preparation of a first generation (G1) PPI dendrimer functionalized by 4-hydroxycoumarin based on the Manich reaction and its use for chromium removal. The literature review showed that dendrimers are large tree molecules constructed by iterative processes from a molecule with at least three reactive sites. These hyper-branched and multi-functional macromolecules have a perfectly defined structure whose applications in various fields such as catalysis, materials, or biology, or even medicine are constantly developing. Indeed, these dendrimers allow the development of new organic/inorganic materials with a controlled structure, but also to modify, at the nanoscale, the surface of existing materials. Coumarins form a set of molecules with multiple beneficial properties including antioxidant, anti-inflammatory, anticancer, antibacterial, antiviral properties. These molecules have also been shown to be good metal ion chelators and are able to modulate MMPs activity. The study of the adsorption of trivalent chromium and hexavalent chromium by the PPI dendrimer functionalized with Coumarin noted C3, shows that the kinetics are carried out in two stages with a high removal yield for Cr (VI) (56.15%) and very low for Cr (III) (12.98%). In this study, an amount of 30mg of adsorbent is used keeping the initial chromium concentration (30mg/L), pH (2), stirring rate, contact time and temperature constant.

Synthesis of second generation dendrimere PPI (G2) functionalized with 4-hydroxycoumarin effective for the removal of chromium (VI) by adsorption

We report here the preparation of a second generation PPI dendrimer (G2) functionalized by 4-hydroxycoumarin based on the Manich reaction and its use for chromium (VI) removal. The literature review has shown that dendrimers are types of polymer defined by regular branches of a central monomer, which give it a tree molecular structure. Their ends carry functional groups whose arrangement gives rise to cavities that are able to receive other molecules as part of host-guest chemistry. To increase the generation or modify peripheral groupings it is possible to manipulate the properties during the synthesis of the dendrimer. Coumarins are a set of molecules with multiple beneficial properties including antioxidant, anti-inflammatory, anticancer, antibacterial, antiviral properties. It has also been shown that these molecules are good metal ion chelators and are able to modulate the activity of metrix metalloproteinases (MMPs). The study of adsorption, on a PPI dendrimer functionalized with Coumarin (C2), trivalent chromium and hexavalent chromium, shows that the kinetics are carried out in two steps with a significant removal efficiency for Cr VI (38.26%) and zero for Cr III. During this study, we kept the initial chromium concentration, pH, stirring rate, contact time and temperature constant and with the same amount of adsorbent (30 mg).