Yaping Dong

A robust bilayer nanofilm fabricated on copper foam for oil–water separation with improved performances

In this work, a facile approach of covalent layer-by-layer assembly was applied to fabricate a bilayer nanofilm which renders roughened copper foam superhydrophobic with robust performances. Before constructing the bilayer nanofilm, the surface of the foam was roughened by using KOH–K2S2O8 as the oxidation system, giving rise to hierarchical structures of flower-like protrusions and petals. A multifunctional polymeric nanofilm, capable of resisting copper corrosion and serving as an activated interface simultaneously, was first introduced onto the copper surface by heating self-assembled monolayers (SAMs) of one triazinedithiolsilane compound (designated as TESPA). Then, perfluorodecyltrichlorosilane (abbreviated as PFDTCS) was anchored onto the TESPA-modified copper surface. Consequently, a bilayer nanofilm of PFDTCS–TESPA is generated on the hierarchical foam that possesses outstanding superhydrophobic capability. The as-prepared foam exhibits excellent reusability and separation efficiency. After fifty recycles, the separation efficiency exceeds 98% while the surface still retains remarkable superhydrophobicity. The improved efficiency and recycle number are outstanding compared to those of similar systems reported previously. X-ray photoelectron spectroscopy (XPS) was conducted to reveal the mechanism of the robust performances of the bilayer-coated foam. The results show that TESPA can react with copper oxide (CuO) through SH groups yielding TESPA SAM. Upon heating, the newly formed disulfide units (–SS–) and siloxane networks (SiOSi) of the TESPA polymeric nanofilm protect the copper; the outward silanol groups (SiOH) endow the surface with activating ability. PFDTCS can covalently bond to the TESPA polymeric nanofilm via these SiOH groups. The specific arrangement of PFDTCS–TESPA and the chemical bonds of Cu(I)S, as well as the three-dimensional (3D) cross-linked textures of –SS– units and SiOSi networks, cooperatively enhance the chemical durability of the bilayer. The design strategy of preparing the bilayer nanofilm via an interlayer (e.g., TESPA as a molecular adhesive displayed in this work) can also be applied in other superhydrophobic systems for improved long-term utilization.

Insight into excitation-related luminescence properties of carbon dots: synergistic effect from photoluminescence centers in the carbon core and on the surface

Excitation-dependent luminescence (EDE) or excitation-independent luminescence (EIE) property of carbon dots (CDs) has attracted considerable attention. For the first time, we found that nitrogen doped CDs possess adjustable EDE and EIE properties by changing the corresponding environmental pH values for photoluminescence (PL) properties. Structural characterizations and property tests demonstrate that the unique photoluminescence properties of CDs can be attributed to the synergistic effect from the PL centers in the carbon core and on the surface. Doping nitrogen into the carbon core improves the emission efficiency of PL centers; these enhanced PL sites can even dominate fluorescence emission. Passivated surfaces of CDs modified with amino groups not only further boost the emission efficiency, but also make energy levels of PL centers more uniform. In addition, the mechanism of synergistic effect is investigated, which opens up the possibility of designing CDs with desirable PL characteristics. Such nitrogen-doped CDs with adjustable excitation-related luminescence properties have potential applications in detecting acidity or alkalinity of a certain physiological environment by intuitively observing the change in the wavelength.

Functional group effect on flame retardancy, thermal, and mechanical properties of organophosphorus-based magnesium oxysulfate whiskers as a flame retardant in polypropylene

In this paper, magnesium oxysulfate whiskers (MOSw) were reacted with dodecyl dihydrogen phosphate (DDP) to prepare DDP functionalized MOSw (DDPMOSw). The morphology and structure of DDPMOSw were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Then MOSw and DDPMOSw were respectively incorporated into polypropylene (PP) to obtain hybrid composites via the melt mixing method. SEM results showed that the DDPMOSw were distributed more evenly within the PP matrix than MOSw, resulting in the improved thermal stability, nominal strain at break, and impact toughness of PP/DDPMOSw in comparison with PP/MOSw. The flammability of the composites was investigated using limiting oxygen index (LOI) and cone calorimetry (CC) tests. The results showed that the introduction of DDPMOSw into the PP matrix further increased the LOI, meanwhile, reducing the heat release rate (HRR), smoke production rate (SPR) and CO and CO2 release. SEM and energy dispersive spectroscopy (EDS) analyses of the char residues implied two reasons for the more efficient flame-retardant properties of PP/DDPMOSw than PP/MOSw: (i) DDPMOSw was more thoroughly decomposed to release more nonflammable gases and absorb more heat during the combustion process (gas-phase flame-retardant effect); (ii) DDP induced the formation of the carbonaceous residue, leading to a compact and coherent char based on MgO whiskers backbone (condensed-phase flame-retardant effect). Besides, FTIR results indicated that the phosphorous compound layer in the condensed phase also acted as a protective shield.

Effects of different compatilizers on mechanical, crystallization and thermal properties of polypropylene/magensium oxysulfate whisker composites

Abstract Two kinds of compatilizers, maleic anhydride grafted polyolefin elastomer (POE-g-MAH) and maleic anhydride grafted polypropylene (PP-g-MAH), were incorporated into a polypropylene/magnesium oxysulfate whisker (PP/MOSw) composite. Scanning electron microscopy pictures presented a clear interface between MOSw and the PP matrix in the PP/MOSw composite, while vague interfaces appeared in the PP/iPOE-g-MAH/5MOSw and PP/iPP-g-MAH/5MOSw composites. Dynamic mechanical thermal analysis results indicated that PP-g-MAH was highly compatible with the PP matrix while POE-g-MAH was not. Impact strength results showed that POE-g-MAH had a superior toughening effect on PP/MOSw composites, since the proper interfacial interaction and appearance of β-crystal PP. However, incorporating PP-g-MAH seemed to be conducive to increasing strength and modulus (both for tensile and flexural tests), as evidenced by the greatly raised interfacial adhesion between the PP matrix and MOSw. Quantitative characterization carried out by Turcsányi equation for ternary composites also confirmed that PP-g-MAH efficiently enhanced interfacial interaction, by the proof of higher B values. Therefore, the thermal stability of PP-g-MAH treated composites was far superior to that of PP/iPOE-g-MAH/5MOSw composites. Differential scanning calorimetery and polarized light microscopy results showed that POE-g-MAH promoted PP nucleation, with effects further enhanced with the presence of PP-g-MAH.

Effects of different compatibilizing agents on the interfacial adhesion properties of polypropylene/magnesium oxysulfate whisker composites

The effects of maleic anhydride-grafted polypropylene (PP-g-MAH) and maleic anhydride-grafted polyolefin elastomer (POE-g-MAH) on interfacial adhesion properties of the polypropylene/magnesium oxysulfate whiskers (PP/MOSw) composites were investigated via mechanical, thermal, ATR-FTIR and rheological tests. Although significant increases in yield strength and Young’s modulus were observed in PP-g-MAH treated composites, a sharp decline in these properties was observed in POE-g-MAH treated composites. ATR-FTIR results indicated that esterification occurred between the hydroxyl groups of MOSw and the carbonyls of anhydrides of both compatibilizers but POE-g-MAH was still incompatible with the PP matrix, as verified by the presence of shoulder peaks in DTG curves and numerous voids in SEM micrographs. On the other hand, PP-g-MAH was highly compatible with the PP matrix, as evidenced by the peaks in DTG curves and vague interfaces with wrapped melts on the surface of MOSw. Rheological behaviors also confirmed that introducing PP-g-MAH resulted in a transition from liquid-like to solid-like, which was attributed to the stronger interfacial adhesion between MOSw and the PP matrix. POE-g-MAH treated composites, in contrast to PP-g-MAH, maintained liquid-like rheological behaviors as typical molten polymers. There is likely a MOSw network formed in the PP/15PP-g-MAH/15MOSw composite as suggested by the significant deviation of G′ versus G″ plots and the two crossover frequencies observed in plots of tanδ versus frequency.

Preparation of α-Fe2O3 hollow spheres, nanotubes, nanoplates and nanorings as highly efficient Cr(VI) adsorbents

α-Fe2O3 nanoparticles with different morphologies, such as hollow spheres, nanotubes with a limited amount of the {0001} plane exposed, and nanoplates and nanorings with the {0001} plane predominantly exposed, have been synthesised by using NaH2PO4 and urea in a facile hydrothermal method. The mechanism of the morphology evolution from hollow sphere to nanoring has been investigated. It is proposed that the polymerisation of Fe3+/H2PO4− plays an important role in the formation of these morphologies. The adsorption of Cr(VI) from aqueous solution onto these α-Fe2O3 nanoparticles showed that the α-Fe2O3 with nanoring morphology has the highest removal efficiency, and the adsorption capacity reached 16.9 mg g−1. These results indicate that the adsorption mechanism of Cr(VI) onto hematite nanoparticles is a chemisorption process through doubly and triply coordinated hydroxyl groups on the outer surface of α-Fe2O3.

Synthesis and formation mechanism of pinnoite by the phase transition process

Pinnoite (MgB2O(OH)6) for the first time was synthesized using the solid–liquid–solid conversion method. The effects of reaction time, pH value and concentrations of magnesium and borate were investigated. Pinnoite was synthesized under the optimum condition of 8 mmol hungtsaoite and 1% boric acid solution at 80 °C. The products were determined using X-ray diffraction, Fourier-transform infrared spectroscopy, TG-DSC and a UV–vis spectrometer. The change processes of the surface morphology of pinnoite were investigated using scanning electron microscopy. In addition, the formation mechanism of pinnoite was discussed according to the changes in the content of precipitation and pH value.

A new acentric borate of K2Ba[B4O5(OH)4]2·10H2O: synthesis, structure and nonlinear optical property

A new acentric mixed metal borate of composition K2Ba[B4O5(OH)4]2·10H2O, has been successfully obtained by slow evaporation solution method. The compound crystallizes in the Orthorhombic space group Pna21 (No.33) with a = 16.8668(7) Å, b = 13.0903(5) Å, c = 11.5529(5) Å and Z = 4. [B4O5(OH)4]2− clusters serve as fundamental building unit linking with BaO8, K1O6, K2O7 by common O atoms to form three-dimensional layer structure. The second harmonic generation measurements in the powder samples reveal that the compound exhibits approximately 0.5 times that of KH2PO4 (KDP) and phase matching.

Experimental design in the analysis of interferential effects for the determination of Sr in high Ca/Sr ratio brine by inductively coupled plasma atomic emission spectroscopy technique

The ICP-AES technique and experimental design were employed to precisely determine the content of strontium in high Ca/Sr ratio oil field brine of Qaidam basin (Qinghai province, western China). From the statistical analysis using six factor factorial, it was found that Ca2+ is the significant interfering element for the recovery of strontium. Accurate strontium content was derived by eliminating the interference contribution according to the influencing model. The experimental results indicate that, under optimal conditions, the ICP-AES method for strontium determination has low LOD and LOQ, and the precision and accuracy are good with the relatively standard deviation below 1% and recovery between 98.0% ∼ 105.0%.

Crystallization, mechanical, thermal and rheological properties of polypropylene composites reinforced by magnesium oxysulfate whisker

Polypropylene (PP) composites containing magnesium oxysulfate whisker (MOSw) or lauric acid (LA) modified MOSw (LAMOSw) were prepared via melt mixing in a torque rheometer. The heterogeneous nucleating effect of LAMOSw was clearly observed in polarized light microscopy (PLM) pictures with the presence of an abundance of small spherulites. MOSw exhibited no nucleation effect and formed a few spherulites with large size. Compared with PP/MOSw composites, PP/LAMOSw exhibited better impact strength, tensile strength and nominal strain at break, ascribing to three possible reasons: (i) more β-crystal PP formed, (ii) better dispersity of LAMOSw in PP matrix and (iii) the plasticizing effect of LA. The results of dynamic mechanical thermal analysis (DMTA) indicated that brittleness of the PP matrix at low temperature was improved by the addition of LAMOSw, while the interfacial interactions between MOSw and PP matrix were actually weakened by LA, as evidenced by the higher tanδ values over the entire range of test temperatures. In terms of the rheological properties of the composites, both the η* and G′ at low frequencies increase with the addition of MOSw or LAMOSw, indicating that the PP matrix was transformed from liquid-like to solid-like. However, a network of whiskers did not form because no plateau was found in the G′ at low frequencies. With low filler content, LAMOSw produced a stronger solid-like behavior than MOSw mainly due to the better dispersion of the LAMOSw in PP matrix. However, for highly-filled composites, the η* of PP/LAMOSw at low frequencies was smaller than that of PP/MOSw composite, since the particle-particle contact effect played a major role.