Ordered mesoporous carbon preparation by thein situradical polymerization of acrylamide and its application for resorcinol removal

Preparation of chitosan/sodium alginate/nano cellulose composite for the efficient removal of cadmium (II) cations from wastewater and soil systems

In this study, chitosan/sodium alginate/nano cellulose (CSA-N) nanocomposite hydrogels were prepared using a completely green route and used as sorbents to adsorb Cd²⁺ ions from water and soil systems of an environmental aspect. The sorbents were characterized by FTIR, SEM, and XRD. The influences of initial Cd²⁺ concentration, the presence of nano cellulose, type of the polluted environment, and ionic strength on adsorption and desorption isotherms were investigated. The maximum adsorption capacity of cadmium onto CSA was significantly increased from 2264.9 to 4380.97 μmol/g when the system was changed from soil to water, respectively. While, the maximum adsorption capacity of cadmium onto CSA-N was almost the same in the soil and wastewater systems, i.e., 3419.5 and 3230.3 µmol/g, respectively. The results indicated that Langmuir and Freundlich models provided the best fit for the experimental adsorption data for CSA and CSA-N, respectively. By comparing the amounts of Δq, the difference between adsorption and desorption amounts, the CSA was not economically feasible sorbent at high initial concentrations of Cd²⁺ in the wastewater system, while, CSA-N was demonstrated to be a more efficient adsorbent than CSA for cadmium removal from both the soil and wastewater systems.

Enhanced adsorption of resorcinol onto phosphate functionalized graphene oxide synthesized via Arbuzov Reaction: A proposed mechanism of hydrogen bonding and π-π interactions

Phosphate functionalized graphene oxide (PGO) was successfully prepared by Arbuzov reaction and employed for adsorption of resorcinol from an aqueous phase. The phosphate functional groups were successfully incorporated onto the PGO surface by the formation of P-C bonds as identified by the analysis of FTIR and XPS spectra. The evaluation of adsorption capacity of resorcinol onto PGO exhibited significant improvement of resorcinol removal, achieving an adsorption capacity of 50.25 mg/g in the pH range of 4-7 which was 15 times higher than pristine graphene oxide. The addition of 2.4 M and 5 M NaCl in the adsorption system significantly increased the adsorption capacity towards resorcinol from 50.25 mg/g to 82.10 mg/g and 128.10 mg/g, respectively. Based on kinetics and adsorption isotherm studies, Pseudo-First-Order and Langmuir model are the best model to describe the adsorption process indicating that the adsorption is dominantly controlled by physisorption. The thermodynamic analysis suggested that the adsorption process was the favorable, spontaneous, and endothermic process. Besides, the interplay of hydrogen bonding and π-π interactions is proposed to be the governing physisorption mechanism. The outstanding reusability and better adsorption performance make PGO a promising adsorbent for environmental remediation of resorcinol.

Low-temperature (NO + O2) adsorption performance of alkaline earth metal-doped C-FDU-15

To improve the removal capacity of NO + O₂ effectively, the alkaline earth metal-doped order mesoporous carbon (A-C-FDU-15(0.001) (A = Mg, Ca, Sr and Ba)) and Mg-C-FDU-15(x) (x = 0.001-0.003) samples were prepared, and their physicochemical and NO + O₂ adsorption properties were determined by means of various techniques. The results show that the sequence in (NO + O₂) adsorption performance was as follows: Mg-C-FDU-15(0.001) (93.2 mg/g) > Ca-C-FDU-15(0.001) (82.2 mg/g) > Sr-C-FDU-15(0.001) (76.1 mg/g) > Ba-C-FDU-15(0.001) (72.9 mg/g) > C-FDU-15 (67.1 mg/g). Among all of the A-C-FDU-15(0.001) samples, Mg-C-FDU-15(0.001) possessed the highest (NO + O₂) adsorption capacity (106.2 mg/g). The species of alkaline earth metals and basic sites were important factors determining the adsorption of NO + O₂ on the A-C-FDU-15(x) samples, and (NO + O₂) adsorption on the samples was mainly chemical adsorption. Combined with the results of (NO + O₂)-temperature-programmed desorption ((NO + O₂)-TPD) and in situ diffused reflectance infrared Fourier transform spectroscopy (DRIFTS) characterization, we deduced that there were two main pathways of (NO + O₂) adsorption: one was first the conversion of NO and O₂ to NO₂ and then part of NO₂ was converted to NO₂^- and NO₃^-; and the other was the direct oxidation of NO to NO₂^- and NO₃^-.

Oxide modified aluminum for removal of methyl orange and methyl blue in aqueous solution

Oxide modified Al exhibited a higher efficiency in removing organic dyes in aqueous solution than pristine Al.

The use of artificial neural network (ANN) for modeling adsorption of sunset yellow onto neodymium modified ordered mesoporous carbon

Discharging coloring products in water bodies has degraded water quality irreversibly over the past several decades. Order mesoporous carbon (OMC) was modified by embedding neodymium(III) chloride on the surface of OMC to enhance the adsorptive removal towards these contaminants. This paper represents an artificial neural network (ANN) based approach for modeling the adsorption process of sunset yellow onto neodymium modified OMC (OMC-Nd) in batch adsorption experiments. Neodymium modified OMC was characterized using N₂ adsorption-desorption isotherm, TEM micrographs, FT-IR and XPS spectra analysis techniques. 2.5 wt% Nd loaded OMC was selected as the final adsorbent for further experiments because OMC-2.5Nd showed highest removal efficiency of 93%. The ANN model was trained and validated with the adsorption experiments data where initial concentration, reaction time, and adsorbent dosage were selected as the variables for the batch study, whereas the removal efficiency was considered as the output. The ANN model was first developed using a three-layer back propagation network with the optimum structure of 3-6-1. The model employed tangent sigmoid transfer function as input in the hidden layer whereas a linear transfer function was used in the output layer. The comparison between modeled data and experimental data provided high degree of correlation (R² = 0.9832) which indicated the applicability of ANN model for describing the adsorption process with reasonable accuracy.

Enhanced Pb(II) adsorption onto functionalized ordered mesoporous carbon (OMC) from aqueous solutions: the important role of surface property and adsorption mechanism

Functionalized ordered mesoporous carbon (MOMC-NP) was synthesized by chemical modification using HNO₃ and H₃PO₄ to enhance Pb(II) adsorption. The phosphate functional group represented by P-O-C bonding onto the surface of OMC was verified by FT-IR and XPS. Batch adsorption experiments revealed the improvement of adsorption capacity by 39 times over the virgin OMC. Moreover, the Pb(II) adsorption results provided excellent fits to Langmuir model and pseudo-second-order kinetic model. The adsorption mechanism of Pb(II) onto MOMC-NP revealed the formation of metal complexes with carboxyl, hydroxyl, and phosphate groups through ion exchange reactions and hydrogen bondings. The calculated activation energy was 22.09 kJ/mol, suggesting that Pb(II) adsorption was a chemisorption. At pH>pH_pzc, the main Pb(II) existing species of Pb(II) and Pb(OH)⁺ combine with the carboxyl, hydroxyl, and phosphate functional groups via electrostatic interactions and hydrogen bonding. All these findings demonstrated that MOMC-NP could be a useful and potential adsorbent for adsorptive removal of Pb(II). Graphical abstract.

The effects of carbon disulfide driven functionalization on graphene oxide for enhanced Pb(II) adsorption: Investigation of adsorption mechanism

The surface properties of graphene oxide (GO) have been identified as the key effects on the adsorption of Pb(II) from aqueous solutions in this study. This study reveals the effect of the surface reactivity of GO via Carbon Disulfide (CS₂) functionalization for Pb(II) adsorption. After successfully preparing CS₂ functionalized GO (GOCS), the specific techniques were applied to investigate Pb(II) adsorption onto GOCS. Results indicated that the new sulfur-containing functional groups incorporated onto GOCS significantly enhanced Pb(II) adsorption capacity on GOCS than that of GO, achieving an improvement of 31% in maximum adsorption capacity increasing from 292.8 to 383.4 mg g^-1. The equilibrium adsorption capacity for GOCS was 280.2 mg g^-1 having an improvement of 83.2% over that of 152.97 mg g^-1 for GO at the same initial concentration of 150 mg L^-1 under the optimal pH of 5.7. Moreover, the results of adsorption experiments showed an excellent fit to the Langmuir and Pseudo-Second-Order models indicating the monolayer and chemical adsorption, respectively. The mechanism for Pb(II) adsorption on GOCS was proposed as the coordination, electrostatic interactions, cation-pi interactions, and Lewis acid-base interactions. The regeneration study showed that GOCS had an appreciable reusability for Pb(II) adsorption with the adsorption capacity of 208.92 mg g^-1 after five regeneration cycles. In summary, GOCS has been proved to be a novel, useful, and potentially economic adsorbent for the high-efficiency removal of Pb(II) from aqueous solutions.

Modeling mass transfer for adsorptive removal of Pb(II) onto phosphate modified ordered mesoporous carbon (OMC)

Phosphate modified ordered mesoporous carbon (MOMC-NP) has been synthesized and proven to be an effective adsorbent for Pb(II) removal from aqueous solutions. However, the key application components of the mass transfer operations and diffusion coefficient have not been determined. In this study, a modified Finite Bath Diffusion Control Model was mathematically developed containing a constant related to the radius of the adsorbent particle and the fractional attainment of adsorption. The adsorption experiments were conducted under various initial Pb(II) concentrations ranging from 60 mg L^-1 to 100 mg L^-1. The results suggested that the modified Finite Bath Diffusion Control Model was more applicable to the experimental data than the original Finite Bath Diffusion Control Model. The average value of the diffusion coefficient (λD¯) obtained from the modified finite bath diffusion control model was 1.63 × 10^-2 cm² s^-1 indicating the effective diffusivity in the adsorption of Pb(II) on MOMC-NP. Overall, the modified Finite Bath Diffusion Control Model exhibited the precise description and simulation of the mass transfer kinetics for Pb(II) adsorption onto MOMC-NP. Therefore, the modified Finite Bath Diffusion Control Model could be effectively used to investigate the mass transfer kinetics of the adsorption process.

Adsorption performance of CMK-3 and C-FDU-15 in NO removal at low temperature

CMK-3 and C-FDU-15 samples were synthesized using hard-templating and evaporation-induced self-assembly (EISA) methods, respectively. The pore structures of CMK-3 and C-FDU-15 as well as commercial activated carbon were characterized by means of X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and N₂ adsorption-desorption. Adsorption of NO was investigated by means of thermogravimetric analysis, temperature-programmed desorption of NO + O₂, and in situ diffuse reflectance Fourier transform infrared spectroscopy. The results show that the CMK-3 and C-FDU-15 materials possessed ordered and uniform structures. The co-adsorption capacity of NO and O₂ decreased in the sequence CMK-3 (88.6 mg/g) > C-FDU-15 (71.7 mg/g) > AC (25.3 mg/g). There were two main adsorption species on CMK-3 and C-FDU-15: nitrite and nitrate. Nitrite is converted to nitrate easily. However, the adsorption species were more complex on AC, with nitrite being the main species. Moreover, CMK-3 and C-FDU-15 exhibit excellent regeneration efficiency compared with AC. The excellent NO adsorption performance of CMK-3 and C-FDU-15 was associated with their ordered mesoporous structures and high surface areas. The research provides more options for NO adsorption in the future.

Combined effects of textural and surface properties of modified ordered mesoporous carbon (OMC) on BTEX adsorption

In this study, we first investigated the effects of textural parameters and surface properties of ordered mesoporous carbon (OMC) for the adsorptive removal of Benzene, Toluene, Ethylbenzene, and Xylene (BTEX) from aqueous solutions. The BET surface area, pore volume, and surface functional groups of OMC played a crucial role in affecting the adsorption performance of BTEX. Boric acid was used to increase the pore size and BET surface area of OMC from 5.94 nm to 6.74 nm and from 1276 m²/g to 1428 m²/g, respectively. Citric acid was used to introduce more oxygen-containing functional groups on the surface of OMC achieving an overall increase of 11.4% of the oxygen content. The batch adsorption experiments were conducted to evaluate the adsorption capacity for OMC and modified towards BTEX and the results showed that modified OMC exhibited a significant improvement for BTEX removal in the following order: Xylenes > Ethylbenzene > Toluene > Benzene. The BTEX adsorption capacities were improved from 8% to 15% with the addition of boric acid compared to the virgin. Surface functionalized using citric acid exhibited the total adsorption capacity of 142 mg/g with an increment of 40.5% compared to virgin OMC.

Chitosan cross-linked with κ-carrageenan to remove cadmium from water and soil systems

In this study, magnetic bio-adsorbent based on chitosan with high molecular weight was prepared. To stabilize under acidic condition, the synthesized magnetic chitosan was cross-linked with κ-carrageenan (mChitoCar). The magnetic bio-adsorbent was characterized by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The results indicated that mChitoCar had desirable magnetic-sorption properties, and magnetic/bio-adsorbent was successfully synthesized and cross-linked. The present nanocomposite was applied to remove and immobilize Cd2+ from water and soil systems. Adsorption and desorption of cadmium by the chitosan bio-adsorbent were investigated using batch experiments. Isotherm data were described by using Freundlich, Langmuir, Dubinin-Radushkevich, and Temkin models, and better fitting was introduced by Freundlich model in both water and soil systems. The maximum adsorption capacity (b) of cadmium onto mChitoCar appeared to increase from the water system to the soil system, from 750.2 to 992.7 μmol/g, respectively. The adsorption mechanism with the help of potential theory indicates the adsorption of cadmium onto the mChitoCar surface is following chemical adsorption type. To evaluate the efficiency of the modified chitosan as a good bio-adsorbent in water and soil system, the difference between adsorption and desorption amounts, Δq, was calculated. By comparing the amounts of Δq, the bio-adsorbent is not economically feasible at high initial concentrations in the water system. But, the bio-adsorbent used can be relatively economic as a soil modifier.

Adsorptive removal of resorcinol on a novel ordered mesoporous carbon (OMC) employing COK-19 silica scaffold: Kinetics and equilibrium study

Phenolic compounds and their derivatives have been found in industrial wastewater, which pose threats to the natural environment. Ordered mesoporous carbon (OMC) has been identified as an ideal adsorbent possessing high specific surface area and large pore volume to alleviate these pollutants. A novel ordered mesoporous carbon was prepared using COK-19 template with the cubic Fm3m structure for the first time. Ordered mesoporous silica COK-19 was synthesized and reported in 2015. Sucrose as the carbon precursor was impregnated into the mesopores of silica and converted to carbon through carbonization process using sulfuric acid as a catalyst. Ordered mesoporous carbon was obtained after the removal of silica framework using hydrofluoric acid. Boric acid was employed for the preparation of OMCs with tunable pore sizes in the range of 6.9-16.6 nm. Several characterization techniques such as nitrogen adsorption-desorption isotherms, transmission electron microscope (TEM), Fourier transform infrared spectroscopy, Boehm titration and elemental analysis were employed to characterize the OMCs. The pore size analysis and TEM images confirmed that OMC has replicated the mesostructure of the COK-19. Results obtained from adsorption kinetics and isotherms suggest that the Pseudo-second-order model and Langmuir isotherm well described the experimental data.

Molecular simulation and experimental validation of resorcinol adsorption on Ordered Mesoporous Carbon (OMC)

Numerous research works have been devoted in the adsorption area using experimental approaches. All these approaches are based on trial and error process and extremely time consuming. Molecular simulation technique is a new tool that can be used to design and predict the performance of an adsorbent. This research proposed a simulation technique that can greatly reduce the time in designing the adsorbent. In this study, a new Rhombic ordered mesoporous carbon (OMC) model is proposed and constructed with various pore sizes and oxygen contents using Materials Visualizer Module to optimize the structure of OMC for resorcinol adsorption. The specific surface area, pore volume, small angle X-ray diffraction pattern, and resorcinol adsorption capacity were calculated by Forcite and Sorption module in Materials Studio Package. The simulation results were validated experimentally through synthesizing OMC with different pore sizes and oxygen contents prepared via hard template method employing SBA-15 silica scaffold. Boric acid was used as the pore expanding reagent to synthesize OMC with different pore sizes (from 4.6 to 11.3 nm) and varying oxygen contents (from 11.9% to 17.8%). Based on the simulation and experimental validation, the optimal pore size was found to be 6 nm for maximum adsorption of resorcinol.

Activated carbons from avocado seed: optimisation and application for removal of several emerging organic compounds

In this study, avocado seed was successfully used as raw material for producing activated carbons by conventional pyrolysis. In order to determine the best condition to produce the activated carbons, a 2² full-factorial design of experiment (DOE) with three central points was employed by varying the temperature and time of pyrolysis. The two evaluated factors (temperature and time of pyrolysis) strongly influenced the S_BET, pore volumes, hydrophobicity-hydrophilicity ratio (HI) and functional groups values; both factors had a negative effect over S_BET, pore volumes and functional groups which means that increasing the values of factors leads to decrease of these responses; on the other hand, with regards to HI, both factors caused a positive effect which means that increasing their values, the HI has an enhancement over its values. The produced activated carbon exhibited high specific surface areas in the range of 1122-1584 m² g^-1. Surface characterisation revealed that avocado seed activated carbons (ASACs) have hydrophilic surfaces and have predominantly acidic groups on their surfaces. The prepared ASACs were employed in the adsorption of 25 emerging organic compounds such as 10 pharmaceuticals and 15 phenolic compounds which presented high uptake values for all emerging pollutants. It was observed that the activated carbon prepared at higher temperature of pyrolysis (700 °C), which generated less total functional groups and presented higher HI, was the activated carbon with higher sorption capacity for uptaking emerging organic contaminants. Based on results of this work, it is possible to conclude that avocado seed can be employed as a raw material to produce high surface area and very efficient activated carbons in relation to treatment of polluted waters with emerging organic pollutants.