Synthesis of amino-modified ordered mesoporous silica as a new nano sorbent for the removal of chlorophenols from aqueous media

Contamination of natural water with organic pollutants is a problem of major concern and the demand for effective adsorbents for the removal of toxic compounds is increasing. Present work deals with the adsorption of 2-chlorpphenol (2-CP) and 2,4,6-trichlorophenol (2,4,6-TCP) from aqueous solutions on a new nano sorbent; amino-modified ordered mesoporous silica (APS-MCM-41) material. It was found that APS-MCM-41 shows significant adsorption for 2-CP and 2,4,6-TCP. This might be due to the acid and alkaline interactions among the amino functional groups and chlorophenols. Batch adsorption studies were carried out to study the effect of various parameters like adsorbent dose, pH, initial concentration and contact time. It was found that adsorption of 2-CP and 2,4,6-TCP depends upon the solution pH. From the sorption studies it was observed that the uptake of 2,4,6-TCP was higher than that of 2-CP. Freundlich and Langmuir adsorption isotherms were used to model the equilibrium adsorption data for 2-CP and 2,4,6-TCP.     

New sorbent hydrogels for removal of acidic dyes and metal ions from aqueous solutions

Summary Poly(N-hydroxymethylacrylamide), PHMA, hydrogels were prepared by using N-hydroxymethylacrylamide, HMA, monomer and polyethyleneglycol(400)diacrylate as a crosslinking agent in aqueous medium and then amine groups were incorporated onto PHMA hydrogels by amination reaction with different diamines. The obtained hydrogels were characterized by determination of amine value, hydroxymethyl group content and FTIR spectra. The amine value of hydrogels changed from 2.23 to 4.64 mmol/g by depending on the amine compounds used in amination reaction. Their swelling degree increased at acidic pH values and they showed pH dependent swelling behaviour. They were used as sorbent for removal of indigo carmine and Cu(II) ion, as a model dye molecule and metal ion, respectively, from aqueous solutions. The adsorption properties of the hydrogels were investigated by depending on pH, time and initial indigo carmine or Cu(II) ion concentration. It was seen that the amine group incorporated hydrogels have quite high adsorption rate and adsorption capacity, and their adsorption capacities changed with pH of the solution. Langmuir isotherm model was the best fit for adsorption of both indigo carmine and Cu (II) ion.     

Polymer‐derived ceramic aerogels as sorbent materials for the removal of organic dyes from aqueous solutions

Polymer‐derived SiC and SiOC aerogels have been synthesized and characterized both from the microstructural point of view and as sorbent materials for removing organic dyes (Methylene Blue, MB, and Rhodamine B, RB) from water solutions. Their adsorbent behavior has been compared with a polymer‐derived SiC foam and a commercial mesoporous silica. The aerogels can efficiently remove MB and RB from water solution and their capacity is higher compared to the SiC foams due to the higher surface area. The SiOC aerogel remains monolithic after the water treatment (allowing for an easy removal without the need of a filtration step) and its maximum capacity for removing MB is 42.2 mg/g, which is higher compared to the studied mesoporous silica and many C‐based porous adsorbents reported in the literature. The reason for this high adsorption capacity has been related to the unique structure of the polymer‐derived SiOC, which consists of an amorphous silicon oxycarbide network and a free carbon phase.     

Sorption of reactive dyes from aqueous solutions by ordered hexagonal and disordered mesoporous carbons

In the present study two synthetic mesoporous carbons, a highly ordered CMK-3 sample with hexagonal structure and a disordered mesoporous carbon (denoted DMC) were investigated for the sorption of Remazol Red 3BS (C.I. 239) dye in comparison to three commercial activated carbons and a HMS mesoporous silica with a wormhole pore structure. The structural, porosity and surface characteristics of the materials were evaluated using XRD, TEM, N₂ porosimetry, FT-IR spectroscopy and zeta-potential measurements. Optimal dye sorption occurred at pH ～2. Equilibrium sorption data followed the Langmuir model and showed that the two synthetic mesoporous carbons exhibit higher sorption capacities (q_max ～ 500–580 mg/g at 25 °C) in comparison to the commercial activated carbons which possessed either microporous (Takeda 5A and Calgon carbon) or combined micro-/mesoporous (Norit SAE-2) structures and to the HMS mesoporous silica. Thermodynamic parameters as the change in free energy, enthalpy, and entropy of sorption were also estimated. Kinetic studies were carried out and showed a rapid sorption of dye in the first ca. 30 min while equilibrium was reached after ca. 3 h. The sorption kinetics of dye was best described by a second-order kinetic model. A surfactant enhanced carbon regeneration (SECR) technique was used to regenerate the dye-loaded carbon sorbents.     

Nanocomposite hydrogels for selective removal of cationic dyes from aqueous solutions

Removal of organic dyes from waste water has received a significant attention in recent years. In this work, a set of nanocomposite hydrogels (NHs) were prepared and their capacity to absorb crystal violet (CV), a cationic dye, and acid yellow‐23 (AY), an anionic dye, from aqueous solutions was determined. NHs were prepared by in situ formation of Fe₃O₄ magnetic nanoparticles (MNPs) inside poly(acrylamide‐co‐4‐styrene sulfonic acid sodium salt) (P[AAm‐co‐SSA]) hydrogel matrices. The dye absorption capacity of the magnetic NHs (MNHs) was compared with simple hydrogels (hydrogels or SHs) without the MNPs The prepared hydrogels were characterized by FTIR, XRD, thermogravimetric analysis, high resolution TEM, field emission SEM, and vibrating sample magnetometer measurement. From HRTEM, it was confirmed that the prepared MNPs in hydrogel matrices were in the size range of about 8 to 10 nm. The MNHs showed greater swelling behavior as well as greater removal efficiency of cationic dye from aqueous solutions in comparison to the SHs. With increase of SSA mole percentage, dye removal efficiency was also increased for both types of hydrogels. The present study indicates that the hydrogels containing MNPs can be potentially used as an efficient absorbent material for removal of cationic dyes from waste water. POLYM. ENG. SCI., 56:776–785, 2016. © 2016 Society of Plastics Engineers     

Fly ash as a sorbent for boron removal from aqueous solutions: Equilibrium and thermodynamic studies

ABSTRACT

This study presents the application of fly ash from brown coal and biomass burning power plant as a sorbent for the removal of boron ions from an aqueous solution. The adsorption process efficiency depended on the parameters, such as adsorbent dosage, pH, temperature, agitation time and initial boron concentration. The experimental data fitted well with the Freundlich isotherm model and the maximum capacity was found to be 16.14 mg g^?1. The adsorption kinetics followed the pseudo-second-order model. Also, the intra-particle diffusion model parameters were calculated. Thermodynamic parameters such as change in free energy (ΔG°), enthalpy (ΔH°), entropy (ΔS°) revealed on exothermic nature of boron adsorption onto the fly ash.     

The efficient removal of dyes over magnetic Ni embedded on mesoporous graphitic carbon material

Magnetically separable Ni embedded on graphitic mesoporous carbon (NMC) material was fabricated through a facile “sol–gel” route using glucose, nickle nitrate, poly(ethylene glycol)–poly(propylene glycol)–poly(ethylene glycol) (P123) and tetraethyl orthosilicate as carbon source, catalyst and magnetic precursor, soft template and porogen. The obtained NMC material exhibited highly graphitic degree with high surface area of 790 m² g^?1, large pore size at 3.9 nm and pore volume of 0.69 cm³ g^?1. The saturation magnetization was enhanced to 6.82 emu g^?1 because of aggregation of magnetic Ni particles to clusters. NMC material showed excellent removal to Rhodamine B and the adsorption capacity reached to 168.1 mg g^?1 within 120 min. NMC material could be easily separated by an external magnet and reused after ethanol extraction.     

Utilization of polyampholyte hydrogels for simultaneous removal of textile dyes from aqueous solutions

The study aimed to create hydrogel structures with greater functionality, otherwise known as polyampholytes (PAHs), and to use these in simultaneous removal studies for remazol-type dyes found in environmental waste waters. Adsorption studies were accomplished at 20°C and 35°C, indicated that adsorption process was exothermic in nature. The Q_m values for the PAH-dye systems were in the interval 111–122 mg dye/g PAH with Ads% from 94% to 98%. The ability of PAH hydrogels to adsorb two different species of dye molecules at the same time is an advantage of PAH adsorbents compared to other hydrogel adsorbents prepared in this area.     

Fabrication of three-dimensional ordered macroporous/mesoporous magnesium oxide for efficient cadmium removal

Cadmium (Cd) is a hazardous heavy metal, that poses a serious threat to human health. Magnesium oxide has shown excellent adsorption performance for the removal of Cd(II) from contaminated wastewater. Herein, three-dimensional ordered macroporous/mesoporous MgO (3DOM/m MgO) was synthesized by a double template method using amphiphilic triblock copolymer Pluronic F127 as the soft template and polystyrene colloidal crystal as the hard template. Compared with three-dimensional ordered macroporous MgO (3DOM MgO), 3DOM/m MgO exhibited a macro/mesoporous structure with a larger specific surface area (96.94 m²/g). The maximum adsorption capacity of 3DOM/m MgO reached 2933 mg/g for the removal of Cd(II) removal from an aqueous solution. BET and XPS analyses results revealed that the enhanced Cd(II) adsorption capacity of 3DOM/m MgO was attributed to its large specific surface area and the complexing ability of its hydroxy groups. The adsorption performance of 3DOM/m MgO was investigated by batch adsorption experiments, including adsorption isotherms and adsorption kinetics. 3DOM/m MgO completely removed 100 mg/L Cd(II), with a removal efficiency ≥99.9%. The adsorption behavior followed the pseudo-second-order kinetic model and Langmuir isotherm model, which revealed that the adsorption of Cd(II) on 3DOM/m MgO proceeded via homogeneous chemisorption. Due to its advantages of controllability and excellent adsorption performance, 3DOM/m MgO is a promising adsorbent for the removal of Cd(II) from polluted water.     

Chitosan/polyaniline hybrid for the removal of cationic and anionic dyes from aqueous solutions

Nanostructured chitosan/polyaniline (CH/PANI) hybrid was synthesized via in situ polymerization of aniline in the presence of chitosan. The CH/PANI hybrid was characterized by FTIR spectroscopy, X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy. The CH/PANI hybrid had a nanofibrous structure with an average diameter of 70 nm. This hybrid was employed as an ecofriendly and efficient adsorbent with high adsorption capacity for the removal of Acid Green 25 (AG) and methylene blue (MB) from aqueous solutions. AG and MB were used as anionic and cationic model dyes, respectively. The CH/PANI adsorbent showed high dependence on the pH of the medium with an excellent adsorption performance and regeneration manner. The kinetics and adsorption isotherms were studied. The CH/PANI hybrid follows the pseudo second-order adsorption kinetics and Temkin isotherm model for the adsorption of both AG and MB dyes. This assumes that the enthalpy of dyes molecules decreases with the adsorption on heterogeneous surface with various kinds of adsorption sites and as well as the ability to form multilayers of the dye. Also, intraparticle diffusion was found to play an important role in the adsorption mechanism. The maximum adsorption capacity was found to be 240.4 mg g⁻¹ of AG at pH 4 and 81.3 mg g⁻¹ of MB at pH 11. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47056.     

Utilization of paper mill sludge for removal of cationic textile dyes from aqueous solutions

ABSTRACT

The present study is concerned usage of paper mill sludge (PMS) as an effective adsorbent to remove the two cationic character dyes (Basic Blue 3 [BB3] and Basic Yellow 28 [BY28]) from aqueous solutions. The surface morphology and some characteristics of PMS were determined by Fouirer Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Brunauer Emmett Teller (BET). The parameters affecting the process – temperature (10–55°C), adsorbent dose (0.5–10 g/l), initial pH (2–10 pH), initial concentration (50–250 mg/l) and contact time (0–24 h) – were examined in the batch adsorption experiments. Maximum adsorption capacities (q_max) of two dyes at 1 g/l dose and pH value of 7 were also calculated as 89.35 and 79.81, respectively. Adsorption phenomena of BB3 and BY28 cationic dyes onto PMS is controlled by pseudo-second-order model. Thereafter, equilibrium experimental data were applied to Langmuir, Freundlich and Dubinin–Redushkevich (D-R) isotherms, and Langmuir isotherm is the best represent the equilibrium adsorption process for both dyes. The processes occurred by physical adsorption because of calculated activation values (E_a) of BB3 and BY28 dyes were 19.43 and 9.35 kJ/mol, respectively. In addition, based on thermodynamic calculations such as free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°), the results clearly demonstrated that the adsorption process were of exothermic and spontaneous nature for both dyes. At the light of obtained findings, it can be stated that PMS can be used effectively in removal of cationic dyes from textile wastewaters and is an alternative to commercial adsorbents due to its low-cost and abundance in the paper industries.     

Evaluation of polystyrene anion exchange resin for removal of reactive dyes from aqueous solutions

The Amberlite IRA-900 resin was tested to remove C.I. Reactive Black 5, C.I. Reactive Red 2 and C.I. Reactive Red 120 dyes from solutions. Batch adsorption studies concerning effects of the phase contact time, pH, temperature, the presence of salts and surfactants were run. A pseudo second-order kinetic model was used to evaluate the rate constants. The Langmuir equation provided good fit for the experimental data of the equilibrium adsorption. The studies of dyes uptake using the dynamic method were run. The treatment efficiency of Amberlite IRA-900 to model wastewaters was tested. Desorption experiments by the batch method were performed.     

Nano-TiO2 modified with 2-mercaptobenzimidazole as an efficient adsorbent for removal of Ag(I) from aqueous solutions

Nano-TiO₂ was modified with 2-mercaptobenzimidazole via surfactant activation and used as an adsorbent for the removal of Ag(I) under optimum conditions. The adsorbent was characterized using powder X-ray diffraction and FT-IR spectroscopy. The equilibrium data were fitted to the Langmuir, Freundlich and Temkin isotherm models. Langmuir isotherm describes the adsorption data better than Freundlich isotherm and Temkin. Kinetic studies showed that the pseudo second order kinetic model fits the adsorption kinetic processes well. Maximum adsorption capacity for Ag(I) was 128.2 mg g⁻¹ of nano-TiO₂. The method was successfully applied to the removal of silver from radiology film processing wastewater samples.     

Characterization of functionalized multiwalled carbon nanotubes and application as an effective filter for heavy metal removal from aqueous solutions☆

Filtration efficiency of Ni(II) from aqueous solution using pristine and modified MWCNTs filters was investigated as a function of Ni(II) ion concentration, pH, and filter mass. MWCNTs were synthesized by CVD method and modified using two complementary treatments, purification (using a mixture of hydrochloric acid and hydrogen peroxide) and functionalization (using nitric acid). The effect and mechanism of each treatment on the structural integrity of pristine MWCNTs has been studied. Morphology of the pristine and modified filters was investigated by Raman Spectrometry (RS), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), Fourier Transform Infrared (FTIR) spectrometry and Thermogravimetric analysis. It was found from Raman spec-tra that the ratio of the intensity of D-band to that of G-band decreased by purification process, and increased by functionalization process. The adsorption mechanism of Ni(II) onto the surface functional groups of modified MWCNTs was confirmed by FTIR spectrum. The filtration results showed that the removal efficiency of Ni(II) is strongly dependent on pH and could reach 85%at pH=8. Also, modified MWCNT filters can be reused through many cycles of regeneration with high performance. Functionalized MWCNTs filters may be a promising adsor-bent candidate for heavy metal removal from wastewater.     

PtCo supported on ordered mesoporous carbon as an electrode catalyst for methanol oxidation

A catalyst for methanol oxidation, PtCo supported on graphitized mesoporous carbon, has been synthesized and its electrochemical activity for methanol oxidation has been investigated. The graphitized mesoporous carbon support with ordered pore structure and high surface area of 585 m² g⁻¹ was prepared by one-step melt casting method using Al doped hexagonal mesoporous silica as hard templates and mineral pitches as carbon precursors followed by carbonization at 800 °C. The materials were characterized by X-ray diffraction, Raman spectra, field emission scanning electron microscopy, transmission electron microscopy and nitrogen sorption techniques. Cyclic voltammetry and amperometric i-t tests were adopted to characterize the electro-catalytic activities of the materials for methanol oxidation. The results show that the graphitized mesoporous carbon exhibits large electrochemical capacitance and good electric property. After supported with 20 wt%Pt or 20 wt%PtCo nanoparticles, the resultant mesostructured composites show 26-97% higher electrochemical catalytic activity for methanol oxidation than commercial catalyst 20 wt%Pt/C in mass activity (mA mg Pt⁻¹).     

Highly efficient metal-free phosphorus-doped platelet ordered mesoporous carbon for electrocatalytic oxygen reduction

Platinum-free electrocatalysts especially, various heteroatom-doped carbon nanostructures have attracted particular attraction as plausible solution for commercializing fuel cell technology. In this direction, novel phosphorus-doped platelet ordered mesoporous carbon (P-pOMC) is developed for the first time as metal-free electrocatalyst for alkaline oxygen reduction reaction. The P-pOMC is synthesized by nanocasting method using platelet ordered mesoporous silica as template. Various characterizations reveal that the P-pOMC materials have covalently bound P atoms with carbon framework for facilitation of oxygen reduction reaction (ORR) and also have very high surface area with uniform distribution of short mesoporous channels for unhindered mass transfer. Combination of P doping and excellent surface properties empowers the newly-developed P-pOMC catalyst to show high ORR activity nearly equal to that of state of the art Pt catalyst along with superior long-term stability and excellent methanol tolerance.     

A fast and efficient method for the removal of hexavalent chromium from aqueous solutions

In this study, removal of chromium (VI) from aqueous solution by as-synthesized MCM-48 adsorbent was studied. Cetyltrimethylammonium bromide (CTAB) was used as a cationic template for the synthesis of MCM-48. The extent of adsorption was investigated as a function of solution pH, agitation speed, contact time, adsorbent and adsorbate concentrations, reaction temperature and supporting electrolyte (sodium chloride). Langmuir and Freundlich isotherms were used to model the adsorption equilibrium data. The adsorption of Cr (VI) is found to be maximum at pH values in the range of 1–3. The yielded maximum adsorption capacity of 153.8 mg/g at initial concentration of 800 (mg/L) is well predicted by of the Langmuir isotherm. Compared to the various adsorbents reported in the literature, the surfactant-containing material prepared in this study showed promise for practical applications.     

Ionic liquid based periodic mesoporous organosilica: An efficient support for removal of sunset yellow from aqueous solutions under ultrasonic conditions

The efficiency of an ionic liquid based periodic mesoporous organosilica (PMO-IL) in the removal of sunset yellow from aqueous solutions using ultrasonic assisted adsorption method was investigated. The PMO-IL was first characterized by nitrogen sorption and TEM techniques. The optimized conditions (0.013 g of adsorbent, 32 mg L⁻¹ of sunset yellow at 2 min of sonication time and pH 7) were obtained by central composite design (CCD). Fitting the equilibrium data show the suitability of the Langmuir model with second-order equation to control the kinetic of the adsorption process and good reusability (5 cycles) of PMO-IL for adsorption of dye.