Yuejie Ai

Adsorption of 4-n-Nonylphenol and Bisphenol-A on Magnetic Reduced Graphene Oxides: A Combined Experimental and Theoretical Studies

Adsorption of 4-n-nonylphenol (4-n-NP) and bisphenol A (BPA) on magnetic reduced graphene oxides (rGOs) as a function of contact time, pH, ionic strength and humic acid were investigated by batch techniques. Adsorption of 4-n-NP and BPA were independent of pH at 3.0- 8.0, whereas the slightly decreased adsorption was observed at pH 8.0-11.0. Adsorption kinetics and isotherms of 4-n-NP and BPA on magnetic rGOs can be satisfactorily fitted by pseudo-second-order kinetic and Freundlich model, respectively. The maximum adsorption capacities of magnetic rGOs at pH 6.5 and 293 K were 63.96 and 48.74 mg/g for 4-n-NP and BPA, respectively, which were significantly higher than that of activated carbon. Based on theoretical calculations, the higher adsorption energy of rGOs + 4-n-NP was mainly due to π-π stacking and flexible long alkyl chain of 4-n-NP, whereas adsorption of BPA on rGOs was energetically favored by a lying-down configuration due to π-π stacking and dispersion forces, which was further demonstrated by FTIR analysis. These findings indicate that magnetic rGOs is a promising adsorbent for the efficient elimination of 4-n-NP/BPA from aqueous solutions due to its excellent adsorption performance and simple magnetic separation, which are of great significance for the remediation of endocrine-disrupting chemicals in environmental cleanup.

Coagulation Behavior of Graphene Oxide on Nanocrystallined Mg/Al Layered Double Hydroxides: Batch Experimental and Theoretical Calculation Study

Graphene oxide (GO) has attracted considerable attention because of its remarkable enhanced adsorption and multifunctional properties. However, the toxic properties of GO nanosheets released into the environment could lead to the instability of biological system. In aqueous phase, GO may interact with fine mineral particles, such as chloridion intercalated nanocrystallined Mg/Al layered double hydroxides (LDH-Cl) and nanocrystallined Mg/Al LDHs (LDH-CO3), which are considered as coagulant molecules for the coagulation and removal of GO from aqueous solutions. Herein the coagulation of GO on LDHs were studied as a function of solution pH, ionic strength, contact time, temperature and coagulant concentration. The presence of LDH-Cl and LDH-CO3 improved the coagulation of GO in solution efficiently, which was mainly attributed to the surface oxygen-containing functional groups of LDH-Cl and LDH-CO3 occupying the binding sites of GO. The coagulation of GO by LDH-Cl and LDH-CO3 was strongly dependent on pH and ionic strength. Results of theoretical DFT calculations indicated that the coagulation of GO on LDHs was energetically favored by electrostatic interactions and hydrogen bonds, which was further evidenced by FTIR and XPS analysis. By integrating the experimental results, it was clear that LDH-Cl could be potentially used as a cost-effective coagulant for the elimination of GO from aqueous solutions, which could efficiently decrease the potential toxicity of GO in the natural environment.

Experimental and theoretical studies on competitive adsorption of aromatic compounds on reduced graphene oxides

The individual and competitive adsorption studies of benzene, aniline and naphthylamine on reduced graphene oxides (rGOs) were investigated by batch experiments and theoretical density functional theory (DFT). Experimental results indicate that (1) in all the single, binary, and ternary aromatic compound systems, the sequence of maximum adsorption capacity is naphthylamine > aniline > benzene on rGOs; (2) the overall adsorption capacity of rGOs is in the order of ternary > binary > single system. The DFT calculations indicate that (1) the adsorption energy (Ead) follows the order of Ead (benzene) < Ead (aniline) < Ead (naphthylamine); (2) the binding energy (Ebd) values of aromatic mixtures indicate that the intra-molecular interactions between the aromatic compounds themselves have an important influence on their adsorption on rGOs. The DFT calculations are in good agreement with the batch adsorption results. These findings are very important and useful to understand the mechanisms of adsorption of aromatic compounds on rGOs as well as assessing the effect of the benzene-ring number and polar functional groups on the adsorption of coexisting aromatic compounds on rGOs. The contents are important for the application of rGOs in environmental pollution management.

Macroscopic, Spectroscopic, and Theoretical Investigation for the Interaction of Phenol and Naphthol on Reduced Graphene Oxide

Interaction of phenol and naphthol with reduced graphene oxide (rGO), and their competitive behavior on rGO were examined by batch experiments, spectroscopic analysis and theoretical calculations. The batch sorption showed that the removal percentage of phenol or naphthol on rGO in bisolute systems was significantly lower than those of phenol or naphthol in single-solute systems. However, the overall sorption capacity of rGO in bisolute system was higher than single-solute system, indicating that the rGO was a very suitable material for the simultaneous elimination of organic pollutants from aqueous solutions. The interaction mechanism was mainly π-π interactions and hydrogen bonds, which was evidenced by FTIR, Raman and theoretical calculation. FTIR and Raman showed that a blue shift of C═C and -OH stretching modes and the enhanced intensity ratios of ID/IG after phenols sorption. The theoretical calculation indicated that the total hydrogen bond numbers, diffusion constant and solvent accessible surface area of naphthol were higher than those of phenol, indicating higher sorption affinity of rGO for naphthol as compared to phenol. These findings were valuable for elucidating the interaction mechanisms between phenols and graphene-based materials, and provided an essential start in simultaneous removal of organics from wastewater.

β-Cyclodextrin modified graphitic carbon nitride for the removal of pollutants from aqueous solution: experimental and theoretical calculation study

A novel β-cyclodextrin modified, multifunctional, layer-by-layer graphitic carbon nitride (g-C3N4/β-CD) was successfully synthesized and applied as an effective adsorbent for the removal of methyl orange (MO) and Pb(II) from aqueous solutions under various environmental conditions (e.g., solution pH, solid content, contact time and temperature). The kinetic results indicated that the adsorption was dominated by chemisorption, and the higher adsorption capacity of g-C3N4/β-CD was attributed to it having more oxygen-containing functional groups than g-C3N4. The Langmuir, Freundlich and Sips models were applied to simulate the adsorption isotherms of MO and Pb(II), and the results demonstrated that the adsorption of MO was attributed to multilayer adsorption, while the coverage adsorption of Pb(II) on the g-C3N4/β-CD was monolayer adsorption. The thermodynamic parameters showed that the adsorption of both MO and Pb(II) was spontaneous and endothermic. The DFT calculations further evidenced the surface complexation and electrostatic interaction of Pb(II) on the g-C3N4 and g-C3N4/β-CD, whereas, the interaction of MO with g-C3N4 and g-C3N4/β-CD was mainly attributed to hydrogen bonds and strong π–π interactions. The results demonstrated that g-C3N4/β-CD is a promising material for the efficient removal of organic and inorganic pollutants in environmental pollution remediation.

Experimental and theoretical evidence for competitive interactions of tetracycline and sulfamethazine with reduced graphene oxides

Competitive interactions of common antibiotics (i.e. tetracycline (TC) and sulfamethazine (SMZ)) with reduced graphene oxides (rGOs) were demonstrated by batch experiments, spectroscopic analysis and DFT calculations. The sorption capacities of TC and SMZ are much higher than that of the TC single system and that of the SMZ single system. The sorption isotherms of TC and SMZ on rGOs in single- and binary-solute systems can be satisfactorily fitted by Langmuir and Freundlich models, respectively. The maximum sorption capacities of rGOs at pH 6.0 and 298 K were 219.10 mg g−1 and 174.42 mg g−1 for TC and SMZ, respectively, indicating that the rGOs presented excellent sorption performance for antibiotics. According to SEM, FT-IR, UV-vis and XPS analysis, the highly efficient sorption of TC and SMZ on rGOs was mainly due to the π–π interaction and high surface energy sites derived from defects, edges and groove areas. The DFT calculations indicated that the sorption energy of TC on rGOs (1.12 eV) was higher than that of SMZ (0.70 eV), suggesting higher sorption affinity of rGOs for TC as compared to SMZ. These findings were crucial to efficiently eliminate various antibiotics from aqueous solutions in environmental pollution cleanup.

Ruthenium/Graphene-like Layered Carbon Composite as an Efficient Hydrogen Evolution Reaction Electrocatalyst

Efficient water splitting through electrocatalysis has been studied extensively in modern energy devices, while the development of catalysts with activity and stability comparable to those of Pt is still a great challenge. In this work, we successfully developed a facile route to synthesize graphene-like layered carbon (GLC) from a layered silicate template. The obtained GLC has layered structure similar to that of the template and can be used as support to load ultrasmall Ru nanoparticles on it in supercritical water. The specific structure and surface properties of GLC enable Ru nanoparticles to disperse highly uniformly on it even at a large loading amount (62 wt %). When the novel Ru/GLC was used as catalyst on a glass carbon electrode for hydrogen evolution reaction (HER) in a 0.5 M H2SO4 solution, it exhibits an extremely low onset potential of only 3 mV and a small Tafel slope of 46 mV/decade. The outstanding performance proved that Ru/GLC is highly active catalyst for HER, comparable with transition-metal dichalcogenides or selenides. As the price of ruthenium is much lower than platinum, our study shows that Ru/GLC might be a promising candidate as an HER catalyst in future energy applications.

Complex Roles of Solution Chemistry on Graphene Oxide Coagulation onto Titanium Dioxide: Batch Experiments, Spectroscopy Analysis and Theoretical Calculation

Although graphene oxide (GO) has been used in multidisciplinary areas due to its excellent physicochemical properties, its environmental behavior and fate are still largely unclear. In this study, batch experiments, spectroscopy analysis and theoretical calculations were addressed to promote a more comprehensive understanding toward the coagulation behavior of GO onto TiO2 under various environmental conditions (pH, co-existing ions, temperature, etc.). The results indicated that neutral pH was beneficial to the removal of GO due to the electrostatic interaction. The presence of cations accelerated GO coagulation significantly owing to the influence of electrical double layer compression. On the contrary, the presence of anions improved the stability of GO primarily because of electrostatic repulsion and steric hindrance. Results of XRD, FTIR and XPS analysis indicated that the coagulation of GO on TiO2 was mainly dominated by electrostatic interactions and hydrogen bonds, which were further evidenced by DFT calculations. The high binding energy further indicated the stability of GO + TiO2 system, suggesting that TiO2 can be used as an effective coagulant for the efficient elimination and coagulation of GO from aqueous solutions. These findings might likely lead to a better understanding of the migration and transformation of carbon nanomaterials in the natural environment.

Experimental and theoretical calculation investigation on efficient Pb(II) adsorption on etched Ti3AlC2 nanofibers and nanosheets

Layered 2D etched Ti3AlC2 nanofibers and nanosheets with different morphologies (named as e-TACFs and e-TACSs) were successfully synthesized by a simple hydrothermal treatment. The adsorption of Pb(II) on e-TACFs and e-TACSs under various conditions was found to be strongly dependent on pH and ionic strength. Thermodynamic parameters calculated from temperature-dependent isotherms showed that the adsorption of Pb(II) on both samples was spontaneous and endothermic. Specifically, due to their enhanced specific surface area and complexation affinity with Pb(II), the maximum adsorption capacity of Pb(II) on e-TACFs at pH 5.0 was 285.9 mg g−1, which was higher than that of Pb(II) on e-TACSs (218.3 mg g−1). The interaction mechanisms of Pb(II) with e-TACFs and e-TACSs were mainly attributed to cation exchange and outer-sphere surface complexation, which synergistically promoted the adsorption kinetics and enhanced the adsorption capacity. The DFT computational results were in good agreement with the batch experimental observations. Such a fluoride-free hydrothermal synthesis method and excellent heavy metal removal capacity demonstrate that 2D etched Ti3AlC2 nanomaterials are promising materials for the efficient removal of Pb(II) in environmental pollution remediation.

Coagulation behavior of humic acid in aqueous solutions containing Cs + , Sr 2+ and Eu 3+ : DLS, EEM and MD simulations

The coagulation behaviors of humic acid (HA) with Cs+ (10-500 mM), Sr2+ (0.8-10.0 mM) and Eu3+ (0.01-1.0 mM) at different pH values (2.8, 7.1 and 10.0) were acquired through a dynamic light scattering (DLS) technique combined with spectroscopic analysis and molecular dynamic (MD) simulations. The coagulation rate and the average hydrodynamic diameter () increased significantly as the concentration of nuclides increased. could be scaled to time t as ∝ ta at higher Sr2+ concentrations, which shows that HA coagulation is consistent with the diffusion-limited colloid aggregation (DLCA) model. Trivalent Eu3+ induced HA coagulation at a much lower concentration than bivalent Sr2+ and monovalent Cs+. The coagulation value ratio of Sr2+ and Eu3+ to Cs+ is almost proportional to Z-6, indicating that the HA coagulation process is generally consistent with the Schulze-Hardy rule. Spectroscopic analysis indicated that the complexation between nuclides and carboxylic/phenolic groups of HA molecules played important roles in the coagulation of HA. MD modelling suggested that Sr2+ and Eu3+ ions increased the coagulation process through the formation of intra- or inter-molecular bridges between negatively charged HA molecules, whereas for Cs+, no inter-molecular bridges were formed. This work offers new insight into the interactions between HA and radionuclides and provides a prediction for the roles of HA in the transportation and elimination of radionuclides in severely polluted environments.