Qing-Da An

Dye adsorption of mesoporous activated carbons produced from NaOH-pretreated rice husks

In continuation of previous work on utilizing rice husks, this study aimed to prepare mesoporous activated carbons using residues of sodium hydroxide-pretreated RHs, and then examine their dye adsorption performance. The influences of the activation temperature and activation time on the surface area, pore volume, and pore radius of the activated carbon were investigated based on nitrogen adsorption/desorption isotherms and transmission electron microscopy. The adsorptive behavior of the mesoporous activated carbons obtained under optimum preparation conditions was evaluated using methyleneblue as the model adsorbate. The adsorption kinetics was studied by pseudo-first-and pseudo-second-order models, and the adsorption isotherms were studied by Langmuir and Freundlich models. The pseudo-second-order model and Langmuir isotherm were found to fit well the adsorption characteristics of the as-prepared mesoporous activated carbons. Thermodynamic data of the adsorption process were also obtained to elucidate the adsorption thermo-chemistry between the activated carbons produced from NaOH-pretreated RHs and MB molecules.

Dye removal of activated carbons prepared from NaOH-pretreated rice husks by low-temperature solution-processed carbonization and H3PO4 activation

A coupling of low-temperature sulfuric acid-assisted carbonization and H3PO4 activation was employed to convert NaOH-pretreated rice husks into activated carbons with extremely high surface area (2028 m(2) g(-1)) and integrated characteristics. The influences of the activation temperature and impregnation ratio on the surface area, pore volume of activated carbons were thoroughly investigated. The morphology and surface chemistry of activated carbons were characterized using N2 sorption, FTIR, XPS, SEM, TEM, etc. The adsorption capacity of resulting carbons obtained under optimum preparation conditions was systematically evaluated using methylene blue under various simulated conditions. The adsorption process can be well described by both Langmuir isotherm model and the pseudo-second order kinetics models; and the maximum monolayer capacity of methylene blue was ca. 578 mg g(-1).

One-step fabrication of highly stable, superhydrophobic composites from controllable and low-cost PMHS/TEOS sols for efficient oil cleanup

Facing the issues of significant increase of industrial oily wastewater and frequent accident of oil spills, the developing of efficient and affordable absorbents for improving oil pollution is of practical significance. Herein, several superhydrophobic and superoleophilic materials, utilizing filter paper, filter cloth and polyester sponge as substrates, through facile coating of hybrid SiO2 colloid particles from controllable PMHS-TEOS sol system were presented. These methyl-modified particles not only provided hierarchical micro/nano-scale structure with distinct roughness, but also largely lowered the surface energy of the coated substances, leading to excellent superhydrophobic and superoleophilic surfaces. The modified filter cloths could be applied for oil/water separation owing to the flexible and foldable property; sponges could efficiently absorb oil or organic solvents in situ on account of its low density and high porosity, and meanwhile the absorbed oil could be easily recollected by simple squeezing. It is worth mentioning that both modified filter cloths and sponges exhibited excellent selectivity, high efficiency, outstanding rapidity and remarkable recyclability. More importantly, after treatment of 100 abrasion cycles with metal scalpel and strongly acidic and basic water droplets, the whole WCA values of resultant filter cloths still maintained superhydrophobic character (>150°), illuminating the charming mechanical and chemical stability of sol-gel processed coating with hierarchical roughness and covalently bonded methyl groups. Combining controllable fabrication process and cheap raw precursors, this method enables scalable manufacturing of stable and superhydrophobic substances, which are promising in practical applications involved in oil/water separation and oil sorption.

In situ preparation of uniform Ag NPs onto multifunctional Fe3O4@SN/HPW@CG towards efficient reduction of 4-nitrophenol

Novel protocol towards multifunctional magnetic organic–inorganic core–shell nanostructured catalysts of Fe3O4@SN/HPW@CG–Ag with tailored properties are presented in this work. Such nanocomposites congregate the properties and functions of a single component into a whole. For instance, Fe3O4 cores protected by amino-functionalized SiO2 shell endowed the composites with superparamagnetism (28.6 emu g−1) and thereby facilitate the process of separation and recovery. Phosphotungstic acid, as a bridging agent, provided a strong interaction for the anchoring of glutaraldehyde cross-linked chitosan onto the surface of Fe3O4@SN. More interestingly, chitosan could simultaneously behave as a stabilizer and reductant for the in situ synthesis of “green” Ag NPs without addition of any other reducing agent or organic solvent, and Ag NPs provided the compounds with a catalytic performance. Further the size, loading of Ag NPs and the thickness of the chitosan layer were all controllable. Meaningfully, the as-synthesized catalyst Fe3O4@SN/HPW@CG–Ag exhibited an exceptional catalytic performance for the reduction of 4-nitrophenol in the presence of sodium borohydride (the reaction was accomplished within 7 min) and could be reused at least 10 times with good stability by means of convenient magnetic separation. Thence, the design philosophy of the multifunctional robust Ag-based nanocatalysts may pave the way for the synthesis of other catalyst systems with long-term stability.

Monolithic magnetic carbonaceous beads for efficient Cr(VI) removal from water

Monolithic magnetic carbonaceous materials as adsorbents can provide easy recovery and quickly separate pollutants in wastewater treatment; however, the development of designed fabrication processes remains a great challenge. Herein, a supermagnetic monolithic material was synthesized for the first time via the controllable carbonization of ferric alginate beads, and its Cr(VI) adsorption behaviour was investigated in detail. This new adsorbent was characterized using field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), N2 adsorption–desorption isotherms, X-ray diffraction (XRD), Raman spectroscopy, vibrating sample magnetometry (VSM), zeta potential measurements, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Kinetic and equilibrium studies indicated that the experimental data for Cr(VI) adsorption were best described by pseudo-second-order kinetic and Langmuir models. The maximum adsorption capacity of the material for Cr(VI) was calculated to be 143.20 mg g−1 at room temperature. Evaluation of the thermodynamic parameters (ΔH > 0, ΔS > 0, and ΔG < 0) revealed that the adsorption process was endothermic and spontaneous. The mechanistic studies showed that the adsorption of Cr(VI) likely involved electrostatic attraction and a redox reaction. It was demonstrated that the material was an effective adsorbent for Cr(VI) removal with quick separation; most importantly, compared to conventional powdery adsorbents, this bead-like material could be handled much more conveniently for reuse and scale-up for practical applications, owing to its ease of operation and separation.

Preparation of superhydrophobic materials for oil/water separation and oil absorption using PMHS–TEOS-derived xerogel and polystyrene

Fabrication of suerhydrophobic materials towards oil/water separation and oil absorption has been receiving great attention nowadays, due to the significant increase of industrial oily wastewater and frequent accident of oil spill. In most previous studies, the usage of expensive precursors restricted the wide applications of prepared superhydrophobic materials. In this work, superhydrophobic filter paper, fabric and polyester sponges were fabricated by dip-coating the mixed solution of polystyrene and xerogels, which were prepared with tetraethoxysilane and polymethylhydrosiloxane, based on previous work. The as-fabricated fabric can effectively separate oil and water mixtures and possesses excellent reusability; more significantly, the materials maintained its good hydrophobic and excellent oil/water separation capacity even after ten cycles. Interestingly enough, the stability was provided, as a result, the fabric still exhibited superhydrophobic after 100 abrasion times and showed high repellency towards many liquids with different pH values. Additionally, the coated polyester sponges can quickly absorb various oil and organic liquid, which will offer a practical application for the treatment of seawater or oily wastewater. By contrast, this experiment process is simple and avoided using costly fluoro-chemicals or complicated fabrication process.

Interior multi-cavity/surface engineering of alginate hydrogels with polyethylenimine for highly efficient chromium removal in batch and continuous aqueous systems

Chromium(VI) is a well-known highly toxic metal ion that has serious effects on the environment. Herein, novel functional alginate beads were developed cooperatively using polydopamine (PDA)–polyethylenimine (PEI)-modified CaCO3 composites (solid porogens with amine groups), with PEI acting as a granule interior and surface modification reagent. The hollow cavity structures with high-density reactive sites immobilized favorably into the interior of the alginate capsules and the PEI layers grafted onto the alginate bead surface via cross-linking led to bead-like composites with interior/surface accessible PEI, with the aim of exceptional Cr(VI) removal performance from aqueous conditions. SEM-EDS, TEM, XRD, BET, FT-IR, and XPS analysis were used to characterize these new sorbents. The adsorption properties were investigated using batch adsorption and continuous adsorption processes. The optimally designed adsorbent, namely 0.7-HS-PDA@PEI-SA@PEI, possessed excellent Cr(VI) adsorption capacity, exhibiting a superior experimental uptake capacity of 524.7 mg g−1 for Cr(VI), which was much higher than those of most reported adsorbents. The experimental data fitted well to the Freundlich isotherm and pseudo-second-order kinetic model in a batch experiment. The experimental breakthrough curves obtained under continuous processes were correlated with the Thomas and Adams–Bohart models. Significantly, the reusability experiments showed that 0.7-HS-PDA@PEI-SA@PEI beads exhibited excellent regeneration ability, with no obvious decline in adsorption capacity after five cycles. These results indicated that the newly designed 0.7-HS-PDA@PEI-SA@PEI beads were promising for Cr(VI) removal because of their ultra-high chromium adsorption capacity, rapid adsorption rate, low cost, and facile recovery process.

Sodium alginate-based magnetic carbonaceous biosorbents for highly efficient Cr(VI) removal from water

Sodium alginate-derived magnetic carbonaceous materials (Fe–SA-X, X means heating temperature) were fabricated by carbothermal reduction of ferric alginate, aiming for efficient removal of Cr(VI) from water. The materials were characterized by X-ray diffraction patterns, scanning electron microscopy, transmission electron microcopy, Fourier transform infrared spectra, X-ray photoelectron spectroscopy, nitrogen sorption, and Raman spectrometry. The adsorption conditions for Cr(VI) onto the samples were optimized, and adsorption kinetics and isotherm studies were thoroughly studied. The adsorption data fitted well with the pseudo-second-order model and Langmuir isotherm model. The Fe–SA-800 was much more efficient than both Fe–SA-400 and Fe–SA-600, and the maximum adsorption capacity was calculated to be 86.32 mg g−1 based on the Langmuir model. The adsorption mechanism was fully discussed, and desorption and regeneration experiments showed that Fe–SA-800 could be easily regenerated and reused. The above results showed that resulting magnetic biosorbents are promising for toxic Cr(VI) removal from water.

Versatile hierarchical Cu/Fe3O4 nanocatalysts for efficient degradation of organic dyes prepared by a facile, controllable hydrothermal method

A novel monodispersed hierarchical nanocomposite catalyst of Cu/Fe3O4 was successfully synthesized through a short-time (just 4 h), facile, eco-friendly one-pot hydrothermal method. The as-prepared Cu/Fe3O4 nanocomposite was well characterized and the results showed that the products were spherical in morphology with diameters of about 100 nm. The BET surface area of the nanospheres was 37.16 m2 g−1, indicating that the product showed a porous character, and the major BJH pore size was 3.73 nm. The saturated magnetization of the Cu/Fe3O4 nanospheres was 48.0 emu g−1, which facilitated their separation and recovery with the aid of an external magnet. In addition, the influences of experimental parameters such as the dosage of trisodium citrate dehydrate (Na3Cit) and urea as well as reaction duration time were investigated in detail to fully elucidate the formation mechanism. More charmingly, the Cu/Fe3O4 nanocomposites exhibited excellent catalytic activity towards the reduction of hazardous organic dyes (4-nitrophenol, 4-NP; congo red, CR; methylene blue, MB) in aqueous media in the presence of NaBH4 with very fast kinetics and good stability. The relationship between the Cu precursor addition amount and catalytic ability was also established. Considering the simplicity of the operation procedure, short time, low cost as well as easy recycling of the catalyst, this preparation protocol may shed light on the fabrication of other metal oxide materials; and hopefully, this hierarchical nanocomposite may find potential applications in other domains like heavy metal removal or antibacterial applications.

Facile sol–gel synthesis of thiol-functionalized materials from TEOS-MPTMS-PMHS system

Thiol-functionalized sol–gel materials with porous structures were successfully prepared via co-condensation of tetraethoxysilane, (3-mercaptopropyl)-trimethoxysilane, polymeric polymethylhydrosiloxane in the absence of traditional structure-directing agents under proposed basic conditions. The dependence of textural characteristics on the preparation parameters were investigated employing various techniques as such N2 adsorption/desorption isotherms, SEM, TG-DTG, FT-IR and solid state 29Si MAS NMR measurements. It was shown by these characterizations that thiol-functional groups have been successfully introduced into the porous network and the loadings could be tuned by adjusting the content of corresponding precursor in the gel system. Besides, the as-prepared samples exhibited high surface areas, large pore volume, tunable pore diameters and favorable thermal stability. Adsorption experiments indicated that thiol-incorporated materials have selective adsorption ability toward heavy metal ions from aqueous solutions, and a high capacity in adsorbing heavy metal ion of Pb2+ (up to 99.4%) was observed under optimized experimental conditions.