Junshu Wu

Designed synthesis of hematite-based nanosorbents for dye removal

We report the design and synthesis of two hematite (α-Fe2O3)-based nanomaterials based on effective hydrothermal conversion of chemically metastable K1.33Mn8O16 nanowires (KWs) in Fe(NO3)3 aqueous solution. Insights are gained into the functions of sodium dodecyl benzene sulfonate (SDBS) and the mechanisms for generating large quantities of α-Fe2O3 hollow structures (FHSs) and K1.33Mn8O16@α-Fe2O3 heterostructured nanowires (KFHWs) in solution phase. The controllable growth dynamics allows convenient control over the morphology and production of the hematite-based nanostructures. Adsorption experiments indicate that the resulting hematite-based materials are powerful nanosorbents for swift removal of Congo red from wastewater at room temperature. The adsorption kinetics and adsorption isotherm are also investigated and the findings indicate that the as-prepared KFHW and FHS hold great potential as environmentally friendly filter materials for water purification and organic waste removal.

Controlled fabrication of hierarchical WO3 hydrates with excellent adsorption performance

Hierarchical WO3 hydrates have been synthesized via an ion exchange method using Na2WO4·2H2O as a precursor. The morphologies and phase structures of WO3 hydrates can be controlled by tuning the concentration of Na2WO4·2H2O solution. The as-synthesized urchin-like WO3·0.33H2O and flower-like WO3·H2O possess high specific surface area and numerous adsorption functional groups, such as WO and O–H bonds, on the surface. These characteristics result in excellent adsorption performance for both organic dyes and heavy metal ions from wastewater. The maximum uptake capacities of the urchin-like WO3·0.33H2O for methylene blue and Pb2+ are 247.3 and 248.9 mg g−1, respectively and those of the flower-like WO3·H2O are 117.8 and 315.0 mg g−1, respectively. The formation mechanism of such hierarchical mesoporous urchin-like WO3·0.33H2O and adsorption mechanism are studied in this paper.

α-Fe2O3 nanowires deposited diatomite: highly efficient absorbents for the removal of arsenic

α-Fe2O3 nanowires deposited diatomite was prepared using a precipitation–deposition method with FeCl3 as metal source and (NH2)2CO aqueous solution as precipitating agent. Physicochemical properties of the samples were characterized by means of numerous techniques, and their efficiency for the removal of As(III) and As(V) was determined. It is found that the solution pH value, reaction temperature, reaction time, and FeCl3 concentration had effects on the α-Fe2O3 amount loaded on the diatomite. Parameters, such as adsorbent amount, adsorption time, adsorption temperature, pH value, and initial As(III) or As(V) concentration, could influence the As(III) or As(V) removal efficiency of the α-Fe2O3 nanowires/diatomite sample (prepared with a 8 wt% FeCl3 aqueous solution at pH = 4.5 and 50 °C for 35 h) for the removal of As(III) and As(V). Over the α-Fe2O3/diatomite sample at pH = 3.5, the maximal As(III) and As(V) adsorption capacities were 60.6 and 81.2 mg g−1, and the maximal As(III) and As(V) removal efficiency was 99.98 and 100%, respectively. The Langmuir model was more suitable for the adsorption of As(V), whereas the Freundlich model was more suitable for the adsorption of As(III). The adsorption mechanism of the sample was also discussed.

Flower-, wire-, and sheet-like MnO2-deposited diatomites: Highly efficient absorbents for the removal of Cr(VI).

Flower-, wire-, and sheet-like MnO2-deposited diatomites have been prepared using a hydrothermal method with Mn(Ac)2, KMnO4 and/or MnSO4 as Mn source and diatomite as support. Physical properties of the materials were characterized by means of numerous analytical techniques, and their behaviors in the adsorption of chromium(VI) were evaluated. It is shown that the MnO2-deposited diatomite samples with different morphologies possessed high surface areas and abundant surface hydroxyl groups (especially the wire-like MnO2/diatomite sample). The wire-like MnO2/diatomite sample showed the best performance in the removal of Cr(VI), giving the maximum Cr(VI) adsorption capacity of 101 mg/g.

A nanoporous oxide interlayer makes a better Pt catalyst on a metallic substrate： Nanoflowers on a nanotube bed

To improve the contact between platinum catalyst and titanium substrate, a layer of TiO2 nanotube arrays has been synthesized before depositing Pt nanoflowers by pulse electrodeposition. Dramatic improvements in electrocatalytic activity (3×) and stability (60×) for methanol oxidation were found, suggesting promising applications in direct methanol fuel cells. The 3× and 60× improvements persist for Pt/Pd catalysts used to overcome the CO poisoning problem.

New fluorine-doped H2(H2O)Nb2O6 photocatalyst for the degradation of organic dyes

A new solid niobic acid phase, H2(H2O)Nb2O6, with fluorine (F) doping was crystallized using hydrothermal chemistry. F-doped H2(H2O)Nb2O6 octahedra could function as an efficient heterogeneous catalyst for the photodegradation of organic pollutants in water under UV light irradiation. The high photocatalytic activity of the F-doped H2(H2O)Nb2O6 materials is attributed to a synergistic effect of the specific surface area, the surface characteristics and the crystal structure. Our results suggest novel ways of controlling the crystallization of niobium oxides, further the fundamental understanding of their structure–property relationships, and may lead to their application in fields such as environmental protection and energy production.

Bouquet-like calcium sulfate dihydrate: a highly efficient adsorbent for Congo red dye

A unique bouquet-like calcium sulfate dihydrate (BCSD) was successfully synthesized from calcium chloride and aluminum potassium sulfate in aqueous sodium carboxymethyl cellulose (CMC) solution by means of a metathesis reaction. The morphology and structure of BCSD were characterized by scanning electron microscopy, powder X-ray diffraction and transmission electron microscopy. The adsorption of different organic dyes from aqueous solutions onto the as-synthesized BCSD was then investigated, taking into account the influences of adsorbent dose (1.0–3.5 g L−1), solution pH (5.0–12.0) and adsorption time. The results indicated that the temperature and agitation rate had no effect on the morphology of the samples. With the increase of CMC concentration from 0.10% to 0.50%, lamellar calcium sulfate dihydrate (LCSD) gradually transformed into rod-like calcium sulfate dihydrate (RCSD), and eventually generated BCSD. The as-prepared BCSD was monoclinic with preferential [021] and [041] orientations. Moreover, BCSD selectively adsorbed Congo red (CR) instead of rhodamine B and methyl orange. The adsorption equilibrium process of CR was an exothermic process and could adequately be described by the Langmuir isotherm model. The calculated maximum adsorption quantity (qmax) was 1224.09 mg g−1 at 303.5 K, which was almost 12 times larger than that onto LCSD (100.80 mg g−1). Additionally, the adsorption process of CR was a multi-step process, and the adsorption kinetics could be described in terms of a pseudo-second-order model. From attenuated total reflectance Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy studies it was concluded that CR was chemisorbed on BCSD. These results indicate that BCSD is a promising candidate in wastewater treatment.

Seeding-induced construction of N-doped TiO2-bronze@g-C3N4 two-dimensional binary nanojunctions with enhanced photocatalytic activity

Nitrogen-doped TiO2-bronze@g-C3N4 (TiO2 (B)@g-C3N4) two-dimensional binary heterojunctions were constructed based on seeding-induced growth through a microwave-assisted solvothermal process and subsequent thermal treatment in a vacuum. The morphology of the TiO2 (B) nanosheets could be controlled by tuning the concentration of the Ti precursor, which determined the enhanced photoelectron activity. The optimal photocatalytic activity for the degradation of methyl orange (MO) under low-intensity visible-light illumination was obtained at a TiO2 (B)/g-C3N4 molar ratio of 1 : 1, which was 12.7 and 7.9 times higher than that of pure g-C3N4 and P25, respectively. The photocatalytic activity was further enhanced by about 7.7% after in situ N-doping. The improvement in photocatalytic activity of N-doped TiO2 (B)@g-C3N4 hetero-nanojunctions was attributable to the strong absorption in the visible-light region and better separation of photogenerated electron–hole pairs at the nanojunction interface, a result due to the large contact area between N-doped TiO2 (B) and g-C3N4 nanosheets. We have explained the photocatalytic degradation of MO molecules largely in terms of the direct oxidation by the photogenerated holes and partly by the contribution of the superoxide radicals.

Top-down chemical etching to complex Ag microstructures

Complex silver (Ag) crystals were crystallized by a technically flexible top-down chemical etching method in a solution phase. Microscale shaped Ag particles were first grown via a galvanic displacement of Ag on commercial Nb metal foil. The metastable Ag precursor was chemically active in solution containing NO3− and HF, readily crystallizing complex Ag microstructured crystals by a HNO3-assisted etching. Insights are gained into the functions of HF and the mechanisms of generating large quantities of anisotropically shaped particles in the solution-phase. The crucial influences of HF concentration and reaction time on the morphology of Ag microstructures have also been established. This current top-down chemical route provides an extremely simple, mild, and effective recipe to crystallize Ag, which is also possible to expand to grow more metal crystals with controlled structures and particle morphologies.

MgO-based nanosheets loaded with ZnxMg1−xO nanoparticles with UV light-driven photocatalytic performance

This paper reports the synthesis of MgO-based nanosheets loaded with UV-light absorbed, wurtzite ZnxMg1−xO nanoparticles based on calcining Zn2+-adsorbed Mg(OH)2 precursor, as evidenced by X-ray diffraction, UV-visible, X-ray photoelectron spectroscopy analyses, etc. The surface modification of magnesium oxide (MgO) sheet-like adsorbents by Zn–Mg–O alloys generates photocatalytic activity for the degradation removal of cationic dye Rhodamine B and anionic dye methyl orange under UV light irradiation. These findings provide a route to chemically controlled synthesis of new and highly robust MgO–ZnxMg1−xO materials for water purification. The endowed photocatalysis function of MgO makes it be easily recovered via photodegradation of adsorbed dyes rather than high-temperature calcination, thus extending the applications of MgO in dye wastewater treatment.