Boron-doped graphene nanosheet-supported Pt: a highly active and selective catalyst for low temperature H2-SCR.

A series of boron-doped graphene-supported Pt (Pt/BG) nanosheets were designed and synthesized using a one-step facile hydrothermal method. ICP, XPS, and TPD results confirmed that boron atoms were successfully embedded into the graphene matrix. The selective catalytic reduction of nitric oxide with hydrogen (H2-SCR) was tested over Pt/BG catalysts. The multi-roles of doped-boron were investigated by Raman, BET, CO-chemisorption, H2-TPD, XPS, and NO-TPD. Boron doping led to a higher dispersion and smaller size of Pt nanoparticles, facilitated hydrogen spillover, promoted more metallic Pt formation, and increased both H2 and NO chemisorption, which were attributed to an enhanced Pt nucleation rate over doped-boron, electron donation from boron to Pt, and extra chemisorption sites. The reaction performances (conversion 94.7%, selectivity 90.3%, and TOF 0.092 s-1) were greatly promoted attributing to a bifunctional catalytic mechanism. This work paves the way to modify the structure and tune the chemisorption ability of graphene-based catalysts, and provides novel insights for designing high performance catalysts.

FeOOH-graphene oxide nanocomposites for fluoride removal from water: Acetate mediated nano FeOOH growth and adsorption mechanism.

Fluoride adsorption capacity in water matrices depends highly on the properties of each component of the adsorption system, the most important one of these is the physchemical properties of the adsorbent. Nanoparticle Goethite anchored onto graphene oxide (FeOOH+Ac/GO) and rice spike-like Akaganeite anchored onto graphene oxide (FeOOH/GO) were synthesized via an in-situ hydrolysis procedure and compared their fluoride adsorption performances in order to address the effect of crystalline structure growth induced by acetate sodium (NaAc), one important organic ligand in water and soil. The morphology, crystallinity, surface functional groups, elemental compositions and atomic percentage of the two hybrid graphene based nanocomposites were characterized. In order to evaluate fluoride adsorption capacity and reveal fluoride adsorption mechanism, adsorption kinetics and dynamics, effects of pH, effects of co-existing anions and mass transfer coefficients were comprehensively investigated for two adsorbents in water matrix. The results show that organic ligands like acetate greatly modify the crystalline structure of iron (oxy)hydroxide (FeOOH), thus altered its fluoride adsorption performance and adsorption mechanism. It would be very important to know the interface behaviors of mineral mediated by natural organic ligands in water or soil matrices.

Effects of anodic oxidation of a substoichiometric titanium dioxide reactive electrochemical membrane on algal cell destabilization and lipid extraction.

Efficient algal harvesting, cell pretreatment and lipid extraction are the major steps challenging the algal biofuel industrialization. To develop sustainable solutions for economically viable algal biofuels, our research aims at devising innovative reactive electrochemical membrane (REM) filtration systems for simultaneous algal harvesting and pretreatment for lipid extraction. The results in this work particularly demonstrated the use of the Ti4O7-based REM in algal pretreatment and the positive impacts on lipid extraction. After REM treatment, algal cells exhibited significant disruption in morphology and photosynthetic activity due to the anodic oxidation. Cell lysis was evidenced by the changes of fluorescent patterns of dissolved organic matter (DOM) in the treated algal suspension. The lipid extraction efficiency increased from 15.2 ± 0.6 g-lipidg-algae(-1) for untreated algae to 23.4 ± 0.7 g-lipidg-algae(-1) for treated algae (p<0.05), which highlights the potential to couple algal harvesting with cell pretreatment in an integrated REM filtration process.

Recovering Magnetic Fe3O4-ZnO Nanocomposites from Algal Biomass Based on Hydrophobicity Shift under UV Irradiation.

Magnetic separation, one of the promising bioseparation technologies, faces the challenges in recovery and reuse of magnetic agents during algal harvesting for biofuel extraction. This study synthesized a steric acid (SA)-coated Fe3O4-ZnO nanocomposite that could shift hydrophobicity under UV365 irradiation. Our results showed that with the transition of surface hydrophobicity under UV365 irradiation, magnetic nanocomposites detached from the concentrated algal biomass. The detachment was partially induced by the oxidation of SA coating layers due to the generation of radicals (e.g., •OH) by ZnO under UV365 illumination. Consequently, the nanocomposite surface shifted from hydrophobic to hydrophilic, which significantly reduced the adhesion between magnetic particles and algae as predicted by the extended Derjaguin and Landau, Verwey, and Overbeek (EDLVO) theory. Such unique hydrophobicity shift may also find many other potential applications that require recovery, recycle, and reuse of valuable nanomaterials to increase sustainability and economically viability.

Heteroaggregation between PEI-coated magnetic nanoparticles and algae: effect of particle size on algal harvesting efficiency.

Colloidal interactions between magnetic nanoparticles (NPs) and algal cells are of paramount significance to magnetophoretic separation of algal biomass from water. This study evaluated the size effect of magnetic NPs (MNPs) coated with polyethylenimine (PEI) on the separation efficiency of Scenedesmus dimorphus as well as on the recovery efficiency of MNPs from algal biomass. Results showed that algal harvesting efficiency (HE) increased from ca. 60% to 85% as the diameter of PEI-coated MNPs increased from 9 to 53 nm. Likewise, algal recovery capacity (algae/MNPs, w/w) also showed the same size dependence. But a large size (247 nm) led to a decline of algal HE, which was correctly interpreted by a settling model that predicts large sizes of MNPs could eventually reduce the settling velocity under magnetophoresis. The extended Derjaguin-Landau-Verwey-Overbeek theory revealed that the particle size and PEI coating both influenced the interaction energies (e.g., energy barrier) between MNPs and algae. Particularly, PEI coating significantly reduced the energy barrier between MNPs and algae and thereby increased their heteroaggregation and algal HE. Moreover, PEI-coated MNPs were recovered from the harvested algae biomass through a chemical-free ultrasonic method, and the recovery efficiency appeared to be higher for larger MNPs. Overall, the synthesized sizes of applied MNPs will not only affect algal HE but also have economic implications on magnetophoretic algal separation technologies.

Influences of surface coating, UV irradiation and magnetic field on the algae removal using magnetite nanoparticles.

Magnetophoretic separation is a promising and sustainable technology for rapid algal separation or removal from water. This work demonstrated the application of magnetic magnetite nanoparticles (MNPs) coated with a cationic polymer, polyethylenimine (PEI), toward the separation of Scenedesmus dimorphus from the medium broth. The influences of surface coating, UV irradiation, and magnetic field on the magnetophoretic separation were systematically examined. After PEI coating, zeta potential of MNPs shifted from −7.9 ± 2.0 to +39.0 ± 3.1 mV at a pH of 7.0, which improved MNPs-algae interaction and helped reduce the dose demand of MNPs (e.g., from 0.2 to 0.1 g·g(­1) while the harvesting efficiency (HE) of over 80% remained unchanged). The extended Derjaguin­Landau­Verwey­Overbeek theory predicted a strong attractive force between PEI-coated MNPs and algae, which supported the improved algal harvesting. Moreover, the HE was greater under the UV365 irradiation than that under the UV254, and increased with the irradiation intensity. Continuous application of the external magnetic field at high strength remarkably improved the algal harvesting. Finally, the reuse of MNPs for multiple cycles of algal harvesting was studied, which aimed at increasing the sustainability and lowering the cost.

Photodegradation of Orange II by mesoporous TiO2.

Mesoporous TiO(2) microspheres were prepared by a hydrothermal reaction and are characterized in this paper. Decoloration and mineralization during photodegradation of Orange II by mesoporous TiO(2) at different pH values, formation of sulfate, relative luminosity to luminous bacteria and recycling experiments of the catalyst were studied. The FTIR results further suggested that the novel mesoporous TiO(2) can not only decolor and mineralize dyes completely but also can be effectively reused several times. On the basis of the research, mesoporous TiO(2) would be a promising photocatalyst for practical use.