Mingxuan Yang

Enhanced Adsorptive Removal of Methyl Orange and Methylene Blue from Aqueous Solution by Alkali-Activated Multiwalled Carbon Nanotubes

An alkali-acitvated method was explored to synthesize activated carbon nanotubes (CNTs-A) with a high specific surface area (SSA), and a large number of mesopores. The resulting CNTs-A were used as an adsorbent material for removal of anionic and cationic dyes in aqueous solutions. Experimental results indicated that CNTs-A have excellent adsorption capacity for methyl orange (149 mg/g) and methylene blue (399 mg/g). Alkali-activation treatment of CNTs increased the SSA and pore volume (PV), and introduced oxygen-containing functional groups on the surface of CNTs-A, which would be beneficial to improving the adsorption affinity of CNTs-A for removal of dyes. Kinetic regression results shown that the adsorption kinetic was more accurately represented by a pseudo second-order model. The overall adsorption process was jointly controlled by external mass transfer and intra-particle diffusion, and intra-particle diffusion played a dominant role. Freundlich isotherm model showed a better fit with adsorption data than Langmuir isotherm model. Adsorption interactions of dyes onto CNTs-A from aqueous solutions were investigated using Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), and Brunauer-Emmett-Teller (BET) method. The remarkable adsorption capacity of dye onto CNTs-A can be attributed to the multiple adsorption interaction mechanisms (hydrogen bonding, π-π electron-donor-acceptor interactions, electrostatic interactions, mesopore filling) on the CNTs-A. Results of this work are of great significance for environmental applications of activated CNTs as a promising adsorbent nanomaterial for organic pollutants from aqueous solutions.

One-pot, large-scale synthesis of magnetic activated carbon nanotubes and their applications for arsenic removal

We report a one-pot method to synthesize magnetic iron oxide/CNT composites (MI/CNTs) based on as-prepared CNTs (APCNTs) using KOH activation. MI/CNTs have high specific surface area, good dispersion and magnetic properties, making them promising for use as adsorbents for arsenic removal. The results of this work are highly significant for large-scale applications of APCNTs containing Fe catalytic particles without the need for prior purification.

Water-enhanced Removal of Ciprofloxacin from Water by Porous Graphene Hydrogel.

An environmentally benign and efficient hydrothermal reduction method was applied for the preparation of three-dimensional (3D) porous graphene hydrogel (GH) adsorbents. The physicochemical properties of GH granules were systematically characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectra and Brunauer-Emmett-Teller (BET) method. GH granules showed an excellent adsorption capacity (235.6 mg/g) for ciprofloxacin via combined adsorption interaction mechanisms (e.g. π-π EDA interaction, hydrogen bonding, and hydrophobic interaction). Moreover, reducing the size of the hydrogels can significantly accelerate the adsorption process and enhance the removal efficiency of pollutants from aqueous solution. Water (more than 99 wt%) within hydrogels played a key role in enhancing adsorption performance. The GO hydrogels exhibited an excellent adaptability to environmental factors. These findings demonstrate that GH granules are promising adsorbents for the removal of antibiotic pollutants from aqueous solutions.

One-pot, solid-phase synthesis of magnetic multiwalled carbon nanotube/iron oxide composites and their application in arsenic removal

Carbon nanotubes (CNTs) functionalized with magnetic nanoparticles are attractive for environmental remediation applications due to their high specific surface area conducive for adsorption of water contaminants and the possibility of recovering these nanohybrids after remediation using an external magnetic field. Most of existing methods for synthesizing magnetic iron oxide/CNTs (MIO-CNTs) composites are carried out in the liquid medium and are tedious, uneconomical, and environmentally unfriendly. Herein, we report a one-pot solid-phase route to synthesize MIO-CNTs composites based on pristine CNTs. MIO-CNTs possess a high specific surface area, good dispersibility, and desirable magnetic properties, making them promising as adsorbents for arsenic removal. The maximum arsenic adsorption capacities are 47.41 and 24.05 mg g(-)(1) for As(V) and As(III), respectively. These values are among the highest for carbon-based materials. Oxygen-containing groups on the surface of MIO-CNTs play a crucial role in arsenic adsorption. This work is very important for the practical applications of pristine CNTs containing catalyst nanoparticles without the need of purifications.

A facile one-pot method for synthesis of low-cost magnetic carbon nanotubes and their applications for dye removal

We report a facile one-pot method to produce magnetic carbon nanotubes (MCNTs) using as-prepared carbon nanotubes modified by NaClO. MCNTs were used as adsorbents for the removal of dye pollutants, and the resulting MCNT hybrids exhibit good dispersibility, excellent magnetic and adsorption properties of dyes, which could favor many applications such as in biomedicine, environmental and energy industries.

Self-regenerative adsorbent based on the cross-linking chitosan for adsorbing and mineralizing azo dye

In this work, we synthesized self-regenerative chitosan (SRCS) by combining the photo-catalyst TiO2 and cross-linking chitosan (CS). The novel SRCS hybrids were then used as adsorbents to remove methyl orange (MO) and they demonstrated excellent adsorption capacity (∼799.2 mg g−1) and significant photocatalytic self-regenerative properties. The pseudo-first-order (PFO), pseudo-second-order (PSO) and Weber–Morris kinetics models were applied to fit the experimental data obtained from batch experiments. The PSO kinetic model was more appropriate for describing the adsorption of MO onto the SRCS. Interestingly, the SRCS adsorbent was successfully regenerated by UV photocatalysis after adsorption. More importantly, the adsorption effectiveness of the SRCS remained constant through eight regeneration cycles. This study provides a green method of removing organic pollutants that combines adsorption enrichment with photocatalytic degradation.

Easy solid-phase synthesis of pH-insensitive heterogeneous CNTs/FeS Fenton-like catalyst for the removal of antibiotics from aqueous solution

We report a facile solid method to synthesize efficient carbon-based Fenton-like catalyst (CNTs/FeS) using as-prepared carbon nanotubes (APCNTs), which makes full use of the iron nanoparticles in APCNTs without needless purification. Furthermore, the CNTs/FeS was characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric (TG) and other analysis techniques, and then the CNTs/FeS was used as a Fenton-like catalyst for removing ciprofloxacin from aqueous solution. Response Surface Methodology (RSM) was applied to find the effect of the reaction parameter and the optimum operating condition. Results shows the catalytic reaction had better suitability than previous studies in a wide range of pH values (pH 3-8) and the Fenton-like catalyst CNTs/FeS exhibits good catalytic activity for removing of antibiotic, which be attributed to the synergistic effect of adsorption-advanced oxidation and significantly improves efficiency of advanced oxidation. More importantly, the CNTs/FeS catalyst exhibit good regeneration performance and retains a high catalytic capacity (>75%) even after four reaction cycles. The catalytic mechanism were also studied further, the removal mechanism of ciprofloxacin by a CNTs/FeS heterogeneous Fenton-like process primarily involves three removal pathways occurring simultaneously: (a) adsorption removal by CNTs, (b) Fenton-like degradation catalyzed by FeS, (c) catalytic degradation by CNTs catalyst. And these actions also have synergistic effects for ciprofloxacin removal.

Comparative Study of Graphene Hydrogels and Aerogels Reveals the Important Role of Buried Water in Pollutant Adsorption

Water as the universal solvent has well-demonstrated its ability to dissolve many substances, but buried water inside different nanoporous materials always exhibits some unusual behaviors. Herein, 3D porous graphene hydrogel (GH) is developed as a super-adsorbent to remove different pollutants (antibiotics, dyes, and heavy ions) for water purification. Due to its highly porous structure and high content of water, GH also demonstrated its super adsorption capacity for adsorbing and removing different pollutants (antibiotics, dyes, and heavy ions) as compared to conventional graphene aerogel (GA). More fundamentally, the buried-water enhanced adsorption mechanism was proposed and demonstrated, such that buried water in GH plays the combinatorial roles as (1) supporting media, (2) transport nanochannels, and (3) hydrogen bondings in promoting pollutant adsorption. In parallel, molecular dynamics simulations further confirm that buried water in GH has the stronger interaction with pollutants via hydrogen bonds than other buried alcohols. GH integrates the merit of both graphene (e.g., fine chemical resistance and excellent mechanical property) and hydrogel (e.g., high water content, porous structure, and simple solution-based processability and scalability), giving it promising potential for environmental applications.