Hongwen Yu

Graphene oxide adsorption enhanced by in situ reduction with sodium hydrosulfite to remove acridine orange from aqueous solution

Graphene oxide (GO) is a highly effective adsorbent, and its absorbing capability is further enhanced through its in situ reduction with sodium hydrosulfite as the reductant. Acridine orange is the selected target to eliminate with GO as the adsorbent. Under identical conditions, GO without the in situ reduction showed a maximum adsorption capacity of 1.4 g g(-1), and GO with the in situ reduction provided a maximum adsorption capacity of 3.3 g g(-1). Sodium hydrosulfite converts carbonyl groups on GO into hydroxyl groups, which function as the key sites for the adsorption enhancement.

In situ controllable synthesis of magnetic Prussian blue/graphene oxide nanocomposites for removal of radioactive cesium in water

A simple procedure at room temperature using non-toxic and cost-effective precursors has been developed to prepare magnetic Prussian blue/graphene oxide (PB/Fe3O4/GO) nanocomposites for the removal of radioactive cesium in water. Taking advantage of the combined benefits of GO and magnetic PB nanoparticles, PB/Fe3O4/GO nanocomposites exhibit excellent removal efficiency (over 90% for 50 ppm Cs+) and rapid separation from an aqueous solution by an external magnetic field. In addition, the adsorption behavior of these adsorbents fits well with the Langmuir isotherm and the pseudo-second-order kinetic model. Sorption of 70.25% Cs+ to PB/Fe3O4/GO was finished in less than 30 min, and the maximum adsorption capacity was 55.56 mg g−1. The improved adsorption efficiency and capacity of PB/Fe3O4/GO can be attributed to the anchoring technology, which reduced the aggregation of nanoparticles and increased the effective adsorption surface of the adsorbent. These nanocomposites present a high selectivity to Cs+ and extract it in trace amounts. The removal mechanism of Cs+ was revealed for the first time to be H+-exchange and/or ion trapping. The temperature and pH value both affect the sorption performance. The composites were stable in natural water, seawater, and acidic/basic solutions ranging from pH = 4 (HNO3) to 10 (NaOH) with negligible leaching of Fe.

Graphene oxide caged in cellulose microbeads for removal of malachite green dye from aqueous solution

A simple sol-gel method using non-toxic and cost-effective precursors has been developed to prepare graphene oxide (GO)/cellulose bead (GOCB) composites for removal of dye pollutants. Taking advantage of the combined benefits of GO and cellulose, the prepared GOCB composites exhibit excellent removal efficiency towards malachite green (>96%) and can be reused for over 5 times through simple filtration method. The high-decontamination performance of the GOCB system is strongly dependent on encapsulation amount of GO, temperature and pH value. In addition, the adsorption behavior of this new adsorbent fits well with the Langmuir isotherm and pseudo-second-order kinetic model.

A novel adsorbent obtained by inserting carbon nanotubes into cavities of diatomite and applications for organic dye elimination from contaminated water.

A novel approach is described for establishing adsorbents for elimination of water-soluble organic dyes by using multi-walled carbon nanotubes (MWCNTs) as the adsorptive sites. Agglomerates of MWCNTs were dispersed into individual tubes (dispersed-MWCNTs) using sodium n-dodecyl itaconate mixed with 3-(N,N-dimethylmyristylammonio)-propanesulfonate as the dispersants. The resultant dispersed-MWCNTs were inserted into cavities of diatomite to form composites of diatomite/MWCNTs. These composites were finally immobilized onto the cell walls of flexible polyurethane foams (PUF) through an in situ PUF formation process to produce the foam-like CNT-based adsorbent. Ethidium bromide, acridine orange, methylene blue, eosin B, and eosin Y were chosen to represent typical water-soluble organic dyes for studying the adsorptive capabilities of the foam-like CNT-based adsorbent. For comparisons, adsorptive experiments were also carried out by using agglomerates of the sole MWCNTs as adsorbents. The foam-like CNT-based adsorbents were found to have higher adsorptive capacities than the CNT agglomerates for all five dyes; in addition, they are macro-sized, durable, flexible, hydrophilic and easy to use. Adsorption isotherms plotted based on the Langmuir equation gave linear results, suggesting that the foam-like CNT-based adsorbent functioned in the Langmuir adsorption manner. The foam-like CNT-based adsorbents are reusable after regeneration with aqueous ethanol solution.

Prussian blue caged in spongiform adsorbents using diatomite and carbon nanotubes for elimination of cesium

We developed a spongiform adsorbent that contains Prussian blue, which showed a high capacity for eliminating cesium. An in situ synthesizing approach was used to synthesize Prussian blue inside diatomite cavities. Highly dispersed carbon nanotubes (CNTs) were used to form CNT networks that coated the diatomite to seal in the Prussian blue particles. These ternary (CNT/diatomite/Prussian-blue) composites were mixed with polyurethane (PU) prepolymers to produce a quaternary (PU/CNT/diatomite/Prussian-blue), spongiform adsorbent with an in situ foaming procedure. Prussian blue was permanently immobilized in the cell walls of the spongiform matrix and preferentially adsorbed cesium with a theoretical capacity of 167 mg/g cesium. Cesium was absorbed primarily by an ion-exchange mechanism, and the absorption was accomplished by self-uptake of radioactive water by the quaternary spongiform adsorbent.

Study of Homologous Elements: Fe, Co, and Ni Dopant Effects on the Photoreactivity of TiO2 Nanosheets

Despite sustained effort over the years, additional investigations into the relationship between doping elements and the photocatalytic properties of TiO2 are needed. In this work, Fe‐group(Fe, Co, Ni)‐doped anatase TiO2 nanosheets with exposed {0 0 1} facets are prepared by using a facile solvothermal synthetic route. A change in the type and concentration of the doping element consequently leads to a change in the size and percentage of {0 0 1} facets in the TiO2 nanosheets, and finally causes a significant difference in the photocatalytic activities of the as‐prepared TiO2 samples. In this case, the performance of doped TiO2, which serves as the photocatalyst, is investigated by directly assessing its effect on the photodegradation of azo dyes (methylene blue) under UV and visible light irradiation, respectively. Importantly, for the first time these studies reveal that the order of the activities of the doped TiO2 is Ni>Co>Fe, and the optimal value of the percentage of the doping ions to Ti ions is 0.75 %. Electrochemical impedance spectra, photocurrent, and photoluminescence measurements indicate that the charge separation and transportation rate is mainly influenced by the type and concentration of doping ions, which determines the photodegradation activities of the TiO2 host.

A facile approach of fabricating graphene-encapsulated ZnO microspheres and their synergic effect on photocatalytic performance

A facile approach of fabricating homogeneous graphene (GE)-encapsulated ZnO microspheres (ZnO microspheres@GE) by bubbling, sonicating, freeze drying, and reduction is developed. The transmission electron microscopy results reveal an intimate interface between GE and ZnO. The as-synthesized ZnO microspheres@GE composites exhibit much higher adsorption capability and excellent photocatalytic activity for methylene blue compared with bare ZnO microspheres, which should be attributed to improved carrier transport efficiency and large surface area arising from the graphene encapsulating. Besides of that, due to the characters of non-functionalized and easy reproducibility, it should be extended to synthesis of GE-encapsulated other semiconductors as well.

Fabrication of Z-scheme magnetic MoS2/CoFe2O4 nanocomposites with highly efficient photocatalytic activity

MoS2 thin nanosheets decorated with CoFe2O4 nanoparticles have been successfully synthesized via a simple hydrothermal method. The nanocomposites are characterized by XRD, TEM, HRTEM, BET, XPS, UV-Vis DRS, PL and magnetic property analysis. The Z-scheme mechanism at the interface of MoS2 and CoFe2O4 is formed. When the mass ratio of MoS2 and CoFe2O4 is 1:3, the MoS2/CoFe2O4 nanocomposites present excellent photocatalytic performance. The degradation rate of rhodamine B (RhB) and congo red (CR) is 93.80% and 94.43% in 90 and 50 min, respectively, under visible light irradiation. The highly photocatalytic activity could be mainly ascribed to the formed Z-scheme mechanism which facilitates the separation of photoinduced electron-hole pairs. Besides, the MoS2 thin nanosheets not only provide the most active sites for photocatalytic reactions, but also act as the backing material for CoFe2O4 nanoparticles to effectively disperse and avoid the magnetic aggregation. Moreover, the MoS2/CoFe2O4 nanocomposites present a good recyclability and the degradation rate of RhB and CR is still beyond 82% after seven runs. In addition, the nanocomposites can be easily separated by an external magnet.

High performance and prospective application of xanthate-modified thiourea chitosan sponge-combined Pseudomonas putida and Talaromyces amestolkiae biomass for Pb(II) removal from wastewater

Biosorption using microbes has been proved to be an efficient technology to remove heavy metals from wastewater, whereas the imperfections in mechanical property and separation limit their practical application. In this study, Pseudomonas putida I3 and Talaromyces amestolkiae Pb respectively combined with xanthate-modified thiourea chitosan sponge (PXTCS and TXTCS) were synthesized to investigate the Pb(II) removal ability from solutions. The prepared biosorbents possessed a three-dimensional macroporous structure convenient for separation. Experimental data indicated their biosorption behaviors well followed the pseudo-second-order kinetics and Langmuir isotherm model. The maximum biosorption capacities of PXTCS and TXTCS were 232.03 and 241.61mgg-1 with 40% P. putida I3 and 15% T. amestolkiae Pb, respectively. For the effects of co-existing metal ions on Pb(II) biosorption, the promoting degree followed the sequence: Zn(II)>Na(I)≈K(I)>Ca(II)>Mg(II)≈Al(III)≫Cd(II)>Fe(III). Both prepared biosorbents were effective in removing heavy metals from simulated industrial effluents containing various trace-level heavy metals or high concentration Pb(II).

Novel mesoporous TiO 2 @g-C 3 N 4 hollow core@shell heterojunction with enhanced photocatalytic activity for water treatment and H 2 production under simulated sunlight

A novel mesoporous TiO2@g-C3N4 hollow core@shell heterojunction photocatalyst was engineered for the first time by in situ calcining and growing of cyanamide (CY) on the surface of TiO2. The HTCN-1 possesses good structure and performance when the addition amount of CY is 1 mL. HTCN-1 shows high photocatalytic activity toward congo red (CR), rhodamine B (RhB), phenol and ciprofloxacin (CIP) with degradation efficiencies of 97%, 100%, 73%, and 74%, respectively. HTCN-1 also displays high photocatalytic activity for H2 generation at rate of 7.9 μmol h-1. A possible charger transfer mechanism and photocatalytic degradation mechanism of HTCN-1 are proposed basing on the experiment results. The enhanced photocatalytic activity may be attributed to the higher charge transfer efficiency of photogenerated electron-hole (e--h+) pairs caused by close contacts, a larger interfacial area, and the higher barrier for conduction bending. Whats more, HTCN-1 possesses relatively high stability during the entire photoreaction process. Given the unique spatial structure and superior photocatalytic characteristics of the HTCN-1, there is great potential for applications in water treatment and H2 generation.