Initial Solution pH Value Research Articles

Effect of doped strontium on catalytic properties of La1‒xSrxMnO3 for rhodamine B degradation

A series of La1‒xSrxMnO3 samples were prepared by sol–gel method and used to degrade rhodamine B (RhB) in water. All samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N2 adsorption–desorption, temperature-programmed reduction of H2 (H2-TPR) and temperature-programmed desorption of O2 (O2-TPD). The results show that the degradation of RhB is highly dependent on the initial pH value of solution. Sr doping enhances the degradation ability of LaMnO3 for RhB in the time range of 0–40 min under a strong acidic environment, but all samples exhibit similar degradation rate from 40 to 60 min. In La0.7Sr0.3MnO3–RhB reaction system, there are two different degradation pathways, including N-de-ethylation, chromophore cleavage, ring-opening and mineralization. La1‒xSrxMnO3 (x ≤ 0.3) has the perovskite structure of La–Mn oxides, while La0.6Sr0.4MnO3 exhibits a Sr0.4MnLa0.6O2.98 perovskite phase. Sr doping leads to distortion of rhombohedral crystal structure and increases the relative content of Mn4+. The perovskite structure is stable in strong acidic environment during RhB degradation, but the relative content of Mn4+ and Mn3+ on the material surface changes. Sr doped LaMnO3 achieves specific surface area of 58.8 m2/g and total pore volume of 0.152 cm3/g. Furthermore, Sr2+ doping improves redox properties of La–Mn oxides, and the presence of defects makes oxygen diffusion easier compared with the undoped samples.

One-pot thermal synthesis of Ceria/Montmorillonite composite for the removal of hexavalent chromium from aqueous system

The thermal insertion of ceria into the structural framework of Montmorillonite (Mt) clay and the efficiency in Cr (VI) oxyanions removal from the aqueous medium are reported herein. CeO2/Mt adsorbent was synthesized via a one-pot thermal treatment operation. Fourier Transform Infrared (FTIR), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Energy-Dispersive X-ray (EDX), X-Ray Diffraction (XRD), and Point Zero Charge (PZC) were used for the material characterization. Incorporating cerianite into the clay mineral framework resulted in the overall charge-shift of the Mt/CeO2 composite and improved stability. Experimental data were analyzed using the non-linear kinetic and equilibrium adsorption isotherm equations. The values of the Chi-square (χ2 ≤ 0.1167) showed that Cr (VI) uptake proceeded via chemisorption (similar to Lewis acid-base interaction) and monolayer adsorption. The change in the initial Cr (VI) concentration, the solution ionic strength, and pH value impacted the process efficiency for Cr(VI) removal. At low initial Cr (VI) concentration and initial solution pH value of 5.1, about 100% removal efficiency was achieved within 90 mins. The value of the Langmuir monolayer adsorption capacity obtained was 52.08 mg/g. The as-synthesized CeO2/Mt composite is a promising adsorbent for the treatment of water contaminated with Cr (VI) oxoanions.

The effect of Ca-bearing contents in chitosan on Pb 2+, Cd 2+ and Cu 2+ adsorption and its adsorption mechanism.

The preparation of chitosan has been investigated for more than half century; however, the application of chitosan for heavy metal (HM) adsorption is still under research. This study investigated the effects of chitosan with chemically controlled Ca-bearing contents (CBC) on Pb2+, Cd2+ and Cu2+ adsorption in the solution with the initial pH values of 2.10, 4.14 and 6.13. Highly purified chitosan showed the optimum HM adsorption at the initial pH values of 4.14 and 6.13, and the adsorption mechanism was chemisorption involving valence forces through sharing or exchange of electrons between the chitosan and HM ions. Highly purified chitosan prepared from HCl treated chitin only showed effective for Pb2+, however, those prepared from CH3COOH treated chitin showed effective for Pb2+, Cd2+ and Cu2+ adsorption due to a little amount of CBC. The HM adsorption mechanisms of partly purified chitosan were precipitation due to CBC and biosorption. Chitosan with 73% CBC showed the optimum adsorption of Pb2+ (755mg/g) at an initial pH value of 2.10 while Cd2+ (979mg/g) and Cu2+ (877mg/g) at the initial pH values of 4.14 and 6.13. High Ca(OH)2-bearing chitosan prepared from HCl and H2SO4 treated chtin showed the optimum Cd2+ (978mg/g) and Cu2+ (852mg/g) adsorption at an initial pH value of 2.10. Biosorption isotherm and kinetics models showed that the adsorption data of Pb2+, Cd2+ and Cu2+ onto the surface of chitosan was well-fitted by Langmuir model and Pseudo-second-order model with correlation coefficient (R2 > 0.95 and R2 > 0.91, respectively). Pseudo-second-order model showed that the adsorption capacity strongly depended on CBC in chitosan and initial pH value of HM solution. It is concluded that the HM adsorption by the prepared chitosan is a chemical process that was supported by CBC of chitosan through elevating solution pH value.

PH-mediated synthesis of monodisperse gold nanorods with quantitative yield and molecular level insight

Although gold nanorods (GNRs) have been produced with different dimensions and aspect ratios, the current synthesis methods through seed-mediated growth are far from ideal, for instance, the quality (rod yield) and the quantity (gold conversion) cannot be simultaneously satisfied. More critically, there is no molecular level understanding of the growth mechanism. Here, we solved the problem by employing the stoichiometric ratio of reactants and tuning the reactivity of the reductant through adjusting the initial pH value of the growth solution to achieve both good quality and high quantity simultaneously. We also extended our strategy to other enols besides ascorbic acid, such as phenolic compounds, and found that the optimal pH for GNRs synthesis depends on the structure of the individual compound. The mechanistic insight greatly enriches the toolbox of reductants for GNRs growth and makes it possible to synthesize GNRs at both acidic and basic conditions. An interesting phenomenon is that for most of the phenolic compounds we tested, the morphology of the final products follows the same sphere-rod-sphere trend as the initial pH value of the reaction increases, whether it is under acidic or basic conditions, which cannot be explained by any previously proposed mechanism. The effect of pH is mainly attributed to the regulation of the reduction potential of the reductants, and thus the reaction rate. A model has been proposed to explain the dependence of anisotropic growth of GNRs on the concentration gradient of reactants around the seeds, which is decided by both the reaction rate and diffusion rate.

The Thermal Gelation Behavior and Performance Evaluation of High Molecular Weight Nonionic Polyacrylamide and Polyethyleneimine Mixtures for In-Depth Water Control in Mature Oilfields.

A delayed crosslinked polymer gel was developed for in-depth water control in mature oilfields. The thermal gelation behavior of nonionic polyacrylamide (NPAM) and PEI was investigated, and sodium citrate (NaCit) was selected as a new retarder to prolong the gelation time. The gelation performance of NPAM/PEI gel system can be adjusted by varying NPAM or PEI concentration, and a quadratic model is developed by statistical analysis, which predicts the gelation time of NPAM/PEI gel system. The obtained model shows high significance and good reliability, as suggested by the F-ratio of 175.16 and high adjusted R-square value (0.9732). The addition of NaCit exhibits a good delayed gelation effect on the NPAM/PEI gel system, better than that of NaCl. The decrease of the initial pH value of the gelling solution leads to the weaker gel viscosity and longer gelation time due to the protonation of amine groups on the PEI chains. Increasing temperature results in higher gel viscosity but shorter gelation time. The gel system in the presence of NaCit exhibits good compatibility with injection and formation water. A dense three-dimensional structure was observed in matured NPAM/PEI/NaCit gel, and it could keep stable below 160 °C. The gel system could effectively reduce the permeability (>95%) and restricted the flow of water after matured in natural cores.

Performance evaluation and process simulation for synergetic removal of NOx, CO2 and PM using green alkaline solution in a high-gravity rotating packed bed

The high-gravity rotating packed bed (HiGee RPB) developed here can simultaneously remove multiple air pollutants using alkaline solution, thus achieving the flue gas deep purification. The electric-arc-furnace reduction slag (EAFRS) leachate was then used as the alkaline absorbent in HiGee RPB for assessing the removal efficiencies of nitrogen oxide (NOx), carbon dioxide (CO2) and particulate matters (PM) from flue gas. The results indicated the changes to the CO2 capture was enhanced by increasing the initial PH value of the alkaline solution. In contrast, this value has no significant influence on NOx removal. The suitable NOx removal efficiency ranged from 90.9% to 97.09% at the liquid-to-gas (L/G) ratio of 0.01 and high gravity factor of 58.9 to 368. The precipitated calcium carbonate gained from carbonation via HiGee process exhibited similar physical properties to commercial products. In addition, 95.9% of PM removal efficiency was achieved at the L/G ratio and high gravity factor of 0.03 and 235.4, respectively. This treatment furthermore demonstrated a high efficiency for PM collection of over 90% and balanced the energy consumption. Based on the result, an Aspen simulation and a preliminary cost-benefit analysis were carried out to develop a mass-balance model for this system and determine the favorable operating conditions.

Degradation of Orange II by the Fe0/H2O2 system

The degradation of Orange II by the Fe0/H2O2 system was examined. The effects of Orange II concentration, H2O2 concentration, Fe0 dosage, initial solution pH value on the degradation of Orange II were investigated. The experimental results showed that Fe0 was exhibited high catalytic activity on the activation of H2O2 for the degradation of Orange II. The reactive hydroxyl radical (·OH) produced in the Fe0/H2O2 system was significant the key for the degradation of Orange II. The mechanism of the degradation of Orange II was discussed by the UV-Vis spectra analysis and determining intermediate products of the reaction solution by LC-MS. It was speculated that in the process of oxidative degradation, Orange II was first dissociated into 4-(2-hydroxy-1-naphthylazo) benzenesulfonate, and then its azo structure was oxidized and destroyed by hydroxyl radicals (·OH). Secondly, the reaction solution faded to produce benzenesulfonate and 1, 2-naphthoquinone, and then 1, 2-naphthoquinone was further oxidized by ·OH to phthalate. Finally, phthalate and benzenesulfonate could be further mineralized into CO2, H2O and SO4 2-.

Controllable preparation and functionally graded programming of carbon aerogel

PurposeThe purpose of this work is to controllably synthesize a carbon aerogel with programmable functionally graded performance via a simple and effective strategy.Design/methodology/approachThis work uses polyvinyl alcohol (PVA) via the controllable sol-gel, lyophilization, and carbonization approach to achieve a programmable carbon aerogel. This design has the advantages of low raw material and preparation cost, simple and controllable synthetic process and low carbonization temperature.FindingsThe thermal stability and microstructure of PVA aerogel can be controlled by the crosslinking agent content within a certain range. The crosslinking agent content and the carbonization temperature are the key factors for functionally graded programming of carbon aerogels, including microstructure, oxygen-containing functional groups and adsorption performance. The adsorption ratio and adsorption rate of uranium can be controlled by adjusting initial concentration and pH value of the uranium solution. The 2.5%25 carbon aerogel with carbonization temperature of 350 °C has excellent adsorption performance when the initial concentration of uranium solution is 32 ppm at pH 7.5.Research limitations/implicationsAs a new type of lightweight nano-porous amorphous carbon material, this carbon aerogel has many excellent properties.Originality/valueThis work presents a simple, low cost and controllable strategy for functionally graded programming of novel carbon aerogel. This carbon aerogel has great potential for application in various fields such as uranium recovery, wastewater treatment, sound absorption and shock absorption.

Magnetic metal organic frameworks/graphene oxide adsorbent for the removal of U(VI) from aqueous solution

A well-defined magnetic metal organic frameworks (MOFs)/graphene oxide (Fe3O4@HKUST-1/GO) consisting of magnetic Fe3O4 nanoparticles, HKUST-1 nanocrystal and GO was synthesized through a simple and environmentally friendly approach. Characterizations of Fe3O4@HKUST-1/GO adsorbing U(VI) with high-resolution transmission electron microscopy suggested that the Fe3O4@HKUST-1/GO possessed good stability. The introduction of GO enhanced the ability of particles to uptake U(VI) from aqueous solution. The effects of solution pH, contact time and temperature on U(VI) adsorption were systematically tested by intermittent experiments. The adsorption process can be better described by the Langmuir model and the pseudo-second-order kinetic model. The results showed that the Fe3O4@HKUST-1/GO exhibited good adsorption capacity towards U(VI) at the initial solution pH value of 4.0 and T = 318 K. The X-ray photoelectron spectroscopy was used to analyze the U(VI) removal mechanism. This work represents the application of Fe3O4@HKUST-1/GO as a novel adsorbent to extract U(VI) from contaminated water.

Optimization of microelectrolysis process for treatment ofPNP wastewater by response surface methodology

The simulated p-nitrophenol (PNP) wastewater was treated by micro-electrolysis. The Box-Behnken experimental design model in response surface method was adopted with iron-carbon as a micro-electrolytic filler. Factors such as iron chip dosage, initial pH value of solution and reaction time were used as investigation indexes to study the influence of single factors and their interactions on the PNP wastewater removal rate. The final optimization results show that the experiment has a good removal rate of PNP, with only a small difference from the predicted value. It can be seen that the response surface method is feasible and suitable forthe process optimizion of p-nitrophenol wastewatertreatment by micro-electrolysis, which can be applied to engineering practice through further research and improvement.

Size controllable synthesis and photocatalytic performance of mesoporous TiO2 hollow spheres

Hollow mesoporous TiO2 spheres (THs) were prepared via template-directed deposition of TiO2 nanoparticles on the surface of carbon spheres. The carbon spheres were used as hard templates. Their diameters were controlled by pH adjustment prior to a hydrothermal process. Physical properties, such as crystallinity, optical characteristics, microstructure and surface morphology of the samples were characterized. The results showed that the diameter of the carbon template could be well controlled in the range of 397–729 nm by adjusting the initial pH value of the dextrose solution from 3 to 10. Hollow TiO2 spheres with average diameters ranging from 171 to 668 nm and shell thicknesses ranging from 28 to 47 nm formed by heat treatment at 450 °C. The photocatalytic performance of hollow TiO2 spheres and TiO2 nanoparticles was examined under UVA irradiation using a methyl orange aqueous solution as an artificial dye. The study revealed that the THs synthesized using a dextrose solution at pH 7 had a higher photocatalytic activity compared to other samples since it had the lowest shell thickness and the proper optical band gap of 3.12 eV with the longest lifetime of electron-hole pair separation.

Preparation of LiFe1-xMnxPO4/C cathode materials at a pH of 6.5 using a hydrothermal process with high-temperature calcination

In this study, manganese ion-doped lithium iron phosphate/carbon (LiFe1-xMnxPO4/C, LF1-xMxP/C) composite cathode materials with different Mn2+ doping levels (x = 0,0.03,0.05,0.07, and 0.10) were synthesized using a hydrothermal process combined with high-temperature calcination. Loss during the calcination was compensated for by using 3 at.% of excess lithium. Acetic acid or ammonium hydroxide was used to adjust the initial pH value of the hydrothermal solution to 6.5. The results revealed that the LF0.93M0.07P/C composite cathode material had the most favorable electrochemical performance and delivered the highest discharge capacities at different C-rates: 140.8 mAh/g at 0.2 C, 135.8 mAh/g at 0.5 C, 123.6 mAh/g at 1 C, 101.2 mAh/g at 3 C, 88.1 mAh/g at 5 C, and 69.5 mAh/g at 10 C. In addition, the capacity retention rate of 96.5% for LF0.93M0.07P/C after 100 cycles at 1 C–1 C was higher than the 86.5% for the pristine LiFePO4/C under the same C-rate and cycle number conditions. Moreover, the electrochemical performance of LF0.93M0.07P/C was noticeably improved by adding 1 wt% of graphene. Therefore, an appropriate amount of Mn2+ doping could effectively improve the electrochemical performance of the pristine LiFePO4/C cathode materials, particularly the electrochemical performance at a high C-rate, due to the increase in electronic and ionic transportation attributed to the addition of graphene and substitution of Mn2+ for Fe2+ in LiFePO4/C cathode materials.

Influence of operational parameters on photocatalytic decolorization of a cationic azo dye under visible-light in aqueous Ag3PO4

The Ag3PO4 nanoparticles were facilely prepared via the liquid precipitation method, and the physical property, optical properties, crystalline and morphologic properties were explored using various techniques. The XRD and SEM results show Ag3PO4 nanoparticles possessed the cubic phase structure and spheroid-like morphology with a particle size of about 300–500 nm. Spectra analysis results indicated that nanoparticles prepared had the same functional groups as Ag3PO4 and can absorb visible light with wavelengths less than 530 nm. The photocatalytic degradation of a cationic azo dye methylthionine chloride (MB) using Ag3PO4 as a photocatalyst in aqueous solution has been investigated under visible-light irradiation. The effects of different parameters on the photodegradation of MB were analyzed. During visible light photocatalytic degradation of MB in the water at different pH values by the Ag3PO4 catalyst, the process was found along with a regular dependency between the degradation rate and adsorption capacity. Both the adsorption efficiency and degradation efficiency of MB on Ag3PO4 increased with increasing initial solution pH value. Ag3PO4 nanoparticles show excellent photocatalytic activity against cationic azo dye under visible-light irradiation and are expected to be effective as a promising visible-light photocatalyst for textile-dyeing wastewater remediation.

Photo-assisted heterogeneous Fenton-like process for treatment of PNP wastewater

Abstract The purpose of this study was to investigate the effect of photo-assisted heterogeneous Fenton on p-nitrophenol (PNP) wastewater treatment by a homemade reactor. Supported Fe-Ce/Al2O3 was used as a catalyst and H2O2 as an oxidant to treat simulated p-nitrophenol wastewater under ultraviolet light. The effects of H2O2 dosage, catalyst dosage, initial solution pH value, reaction temperature and reaction time on the removal rate of p-nitrophenol in a photo-assisted heterogeneous Fenton system were determined. According to the relation between the concentration of each component and time, the relation curve is fitted, and then the kinetic equation is established. Finally, we obtained the optimum process conditions to achieve the PNP wastewater removal rate of 98.7%. The degradation of the photo-assisted heterogeneous Fenton method conforms to the first-order kinetic model, and the kinetic equation is . Therefore, photo-assisted heterogeneous Fenton treatment of PNP wastewater is effective and can be used in the treatment of refractory wastewater.

Photocatalytic Degradation of Phenol Using Photodeposited Pt Nanoparticles on Titania.

In this study, the photodeposition synthesized Pt-titania (Pt/P25) photocatalysts with various amount of Pt (0.5-5.0 wt.%) were characterized in detail by Brunauer-Emmett-Teller surface area analysis (BET), inductively coupled plasma with optical emission spectroscopy (ICP-EOS), X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (DRS UV-vis), attenuated total reflection (ATR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the investigated catalysts was studied towards the photocatalytic degradation of phenol. The best performance was obtained for the 3.0 wt.% Pt/TiO₂. The concentration of photocatalyst, the initial phenol concentration and pH value of the reaction solution was studied in detail. The obtained results show that the reaction rate increases with increasing catalyst concentration and decreases with increasing phenol concentration. The highest degradation efficiency was observed for a neutral pH. In overall, the results of this study show that the Pt/TiO₂ photocatalysts can efficiently improve the decomposition of phenol in the presence of UV light.

Novel environmental-friendly nano-composite magnetic attapulgite functionalized by chitosan and EDTA for cadmium (II) removal

Adsorbent preparation of non-toxicity, low cost, large adsorption capacity and outstanding reusability is imperative in purifying Cd-contaminated water. In this work, novel environmental friendly shell-coated magnetic attapulgite, named as attapulgite/CoFe2O4@SiO2-chitosan/EDTA (ATPCFS-CSEs), was successfully prepared by solvothermal and sol-gel process. Chitosan and EDTA were selected to functionalize the magnetic attapulgite to provide abundant amino groups and carboxyl groups. Sodium tripolyphosphate was chosen as non-toxic cross-linker in surface deposition-crosslinking, and subsequently amidation reaction was taken for functionalization by chitosan and EDTA. The adsorbents were characterized by SEM, TEM, XRD, FTIR, VSM, BET and XPS, and the adsorption properties including adsorption isotherm, contact time, adsorbents dosage, pH value of initial solution, competitive ions, desorption experiment and recycling method for repeated use were evaluated. The nano-composite adsorbent exhibited well-defined architecture and paramagnetic behavior. The adsorption behavior agreed well with Langmuir model, and adsorption capacity was up to 127.79 mg/g. High concentration ionic competition experiments showed that the ATPCFS-CSEs has high selectivity. Removal efficiency was still above 88% after 5 cycles. The adsorption mechanism was also discussed. Functional groups complexed with cadmium ions with the formation of stable complexes. ATPCFS-CSEs is an excellent adsorbent for removal and separation of Cd2+ from contaminated water.

Adsorption behavior of hexavalent chromium in aqueous solution by polyvinylimidazole modified cellulose

Developing multifunctional adsorbent materials is an effective solution to hexavalent chromium (Cr (VI)) pollution. In this study, 3D macroporous materials with the synergetic advantages of cellulose and polyvinylimidazole were fabricated through a homogeneous method, and served as effective adsorbents for Cr (VI) elimination in aqueous solution. The physicochemical properties of the designed materials were studied by SEM, FTIR, 13C NMR, XPS, and CHN element analysis, and the results confirmed that imidazole groups were successfully grafted onto the macroporous cellulose. The influences of different water chemistry conditions, including contact time, temperature, initial solution pH value, and coexisting ion concentration, on the adsorption performance of the modified cellulose adsorbents were studied, and the corresponding adsorption mechanism was explored. The optimized adsorbent showed a fast adsorption rate (0.12 g/(mg∙min)), and a high adsorption ability (134 mg/g). The adsorption process was spontaneous and conformed to Langmuir isotherm and pseudo-second kinetic models. The Cr (VI) uptake mechanism of the designed materials was primarily controlled by electrostatic attraction, ion exchange, and redox. These results suggest that cellulose modified with imidazole groups is a promising candidate for the adsorption and detoxification of Cr (VI).

Rapid preparation of terbium-doped titanium dioxide nanoparticles and their enhanced photocatalytic performance.

Further applications of photocatalysis were limited by the high recombination probability of photo-induced electron–hole pairs in traditional titanium dioxide nanoparticles (TiO2 NPs). Herein, we modified them with rare earth metal via a facile sol–gel method, using tetrabutyl titanate as a precursor and terbium (III) nitrate hexahydrate as terbium (Tb) source. The resulting samples with different Tb doping amounts (from 0 to 2%) have been characterized by X-ray diffraction, UV–visible diffuse reflectance spectroscopy, X-ray photo-electron spectroscopy and a scanning electron microscope. The photocatalytic performance of Tb-doped TiO2 was evaluated by the degradation of methylene blue. The effects of Tb doping amount and initial pH value of solution were investigated in detail. The composite with Tb doping amount of 1.0 wt% showed the highest photocatalytic performance. It exhibited approximately three times enhancement in photocatalytic activity with a reaction rate constant of 0.2314 h−1 when compared with that of commercial P25 (0.0827 h−1). In addition, it presented low toxicity on zebrafishes with 96 h-LC50 of 23.2 mg l−1, and has been proved to be reusable for at least four cycles without significant loss of photocatalytic activity. A probable photocatalytic mechanism of Tb-doped TiO2 was proposed according to the active species trapping experiments. The high photocatalytic performance, excellent reusability and low toxicity of Tb-doped TiO2 indicated that it is a promising candidate material in the future treatment of dye wastewater.

Arsenic removal from groundwater in Kütahya, Turkey, by novel calcined modified hydrotalcite.

Since arsenic is highly toxic and carcinogenic, it now causes serious health problems all over the world. Therefore, there is an urgent need to develop new techniques that are cost-effective and easily applicable to remove arsenic from contaminated waters. Layer double hydroxides have the potential to be a good adsorbent to remove arsenic from contaminated waters due to high surface area and high anion exchange capacity. In this paper, arsenic removal from water by calcined Fe-hydrotalcite (CFeHT) known as layered double hydroxide and prepared synthetically with coprecipitation method was researched. The study brings out that the effect of initial solution pH values was limited for the adsorption. The experimental study indicates that the adsorption of arsenic rapidly occured in comparison with other studies. It was determined that the pseudo-second-order kinetic model was more suitable than the first order. In isotherm studies, it was seen that the experimental data were compatible with Langmuir model. In this study was determined that CFeHT has a high arsenic removal potential. And also the concentration of the arsenic solution (600µg/L) has been reduced below the allowable value by the World Health Organization (< 10µg/L). The desorption test indicates that the desorption ratio of As(V) was obtained as 72.7.

Polyamidoamine dendrimers functionalized magnetic carbon nanotubes as an efficient adsorbent for the separation of flavonoids from plant extraction

In this study, amine terminated polyamidoamine dendrimer (PAMAM)-functionalized magnetic multi-walled carbon nanotubes (PAMAM@MCNTs) were prepared as an efficient adsorbent for the separation of flavonoids from plant extraction. The obtained PAMAM@MCNT nanoadsorbents were characterized in detail. Rutin was chosen as a model molecule of flavonoids to investigate the adsorption efficiency of PAMAM@MCNTs. The main influences of several parameters, including contact time, initial solution concentration, pH value, and temperature, were optimized to determine the optimum adsorption conditions. Furthermore, the adsorption kinetic and isotherm models were performed to elucidate the adsorption process. The results showed that PAMAM and Fe3O4 were successfully grafted to the surface of carboxylated CNTs (CNTs-COOH) by characterization via several techniques, such as scanning electron microscopy (SEM), X-ray diffraction spectrometry, vibrating sample magnetometry, and Fourier transform infrared spectra. The PAMAM@MCNTs exhibited high efficiency for the rutin at solution pH = 8.0 and room temperature. Adsorption process could be effectively described by Langmuir adsorption isotherm, and the maximum adsorption capacity was calculated as 56.48 mg/g, whereas a pseudo-second-order model was suitable to explain the kinetics of adsorption. The PAMAM@MCNTs can be effectively regenerated by alkaline dimethyl sulfoxide and reused to at least threefold. Moreover, PAMAM@MCNTs demonstrated potential in various applications as an efficient adsorbent for separating flavonoids from plant extraction. The above-mentioned results provided references for further separation of bioactive components from plant extracts using magnetic nanomaterials.