Haojun Fan

Polyacrylic acid-grafted magnetite nanoparticles for remediation of Pb(II)-contained water

Toxic Pb(II) contaminants in water pose a significant threat to the environment and public health, and thus technologies for Pb(II) remediation are attracting increasing industrial interests. In the present work, polyacrylic acid, offering abundant carboxyl groups capable of coordination with Pb(II) cations, was grafted from the magnetite nanoparticle surface via the bridging function of silane coupling agent for remediation of Pb(II)-contained water. Multiple techniques were employed to characterize the structure of the nanocomposite, and the effects of nanoadsorbent dose, pH value, and temperature on Pb(II) removal capability of the nanocomposite were investigated, respectively. Furthermore, adsorption kinetics and isotherms studies were performed for better understanding the mechanism by which Pb(II) cations were adsorbed. Finally, the feasibility of regenerating the exhausted nanoadsorbent by simply changing pH value was explored. According to these results, we intend to offer an efficient, separable, and reusable magnetic nanoadsorbent that may be a potential candidate for remediating Pb(II) contamination in water.

Remediation of chromium(III)-contaminated tannery effluents by using gallic acid-conjugated magnetite nanoparticles

Potential ecological risks of chromium(III) contaminates in tannery effluents have evoked considerable discussion and re-examination over the future role of chrome tannage, which has been long considered as the foundation of the modern leather industry. Despite previous magnetite-supported adsorbents for chromium removal, few of them were specifically engineered to address trivalent chromium, as well as the composition complexity in tannery effluents. Herein, gallic acid, a natural triphenolic compound capable of coordination to chromium(III), was covalently conjugated onto engineered magnetite nanoparticles via 1-ethyl-3-(3-dimethylaminepropyl) carbodiimide hydrochloride/N-hydroxysuccinimide (EDC/NHS) chemistry, in an effort to design a magnetically separable nanoadsorbent applicable for remediating chromium(III)-contaminated tannery effluents. The structure of the nanoadsorbent was systematically characterized by multiple techniques, and the influence of pH value, adsorbent dose, temperature, and leather-related co-existing substances on its chromium(III) removal potency was investigated, respectively. Also, kinetics, equilibrium, and thermodynamics studies were conducted to decipher the mechanism by which chromium(III) cations were adsorbed. Finally, the feasibility of treating real tannery effluents that also contained high concentrations of sulfides, chlorides, ammonium nitrogen, total suspended solids, chemical oxygen demand (CODCr), and biochemical oxygen demand (BOD) by using the nanoadsorbent designed herein was explored. It was found that the chromium(III) removal percentage was approximately 95.2 ± 1.6%, and the exhausted nanoadsorbent could be conveniently separated from the effluents via a simple magnetic process. By chemical desorption, the nanoadsorbent was regenerable, and reusable for multiple cycles without a significantly compromised adsorption potency. According to these results, we aim at providing an efficient solution that may be a great addition to the ongoing fight against chromium(III) contamination in tannery effluents.

Waterborne polyurethane conjugated with novel diol chain-extender bearing cyclic phosphoramidate lateral group: synthesis, flammability and thermal degradation mechanism

A diol bearing a cyclic phosphoramidate pendant group, namely 2-(5,5-dimethyl-2-oxo-2λ5-1,3,2-dioxaphosphinan-2-ylamino)-2-methyl-propane-1,3-diol (PNMPD) was synthesized and characterized by FTIR and NMR. Subsequently, PNMPD was applied as a flame-retardant chain extender to prepare phosphorus–nitrogen containing waterborne polyurethane (PNWPU), and the influence of PNMPD on the hydrolysis, thermal and flame-retardant properties of PNWPU was investigated. The fabricated PNMPD-based PNWPU shows controllable mechanical properties and maintains the good hydrolysis-resistance property of polyurethane. Thermal stability and flammability analysis demonstrate that though the covalent conjugation of PNMPD induces a slight thermal destabilization effect, it efficiently promotes char formation in PNWPU, as a result, a 27.2% limiting oxygen index (LOI) value and a UL-94 V-0 rating can be achieved with only 12 wt% PNMPD incorporated. Compared with WPU, the peak heat release rate (PHRR), total heat release (THR), peak smoke production rate (PSPR) and total smoke release (TSR) of PNWPU-12, evaluated with cone calorimetry, are decreased by 44.7%, 39.0%, 42.9% and 36.1%, respectively. In addition, the flame retarding mechanism of PNWPU was comprehensively investigated by SEM microscopy, EDX analysis, real time FTIR and TG-FTIR, and results elucidate that these notable reductions in fire hazards are probably attributed to the formation of polyphosphoric acid-rich rugged and intumescent char in the condensed phase, which behaves as a “labyrinth effect” to effectively inhibit the transmission of heat, oxygen and volatile fragments from entering into the flame zone and shield the underlying PNWPU matrix against flame.

Synergistic effect of phosphorus–nitrogen and silicon-containing chain extenders on the mechanical properties, flame retardancy and thermal degradation behavior of waterborne polyurethane

With the aim to keep a balance between the flame retardancy and thermal stability as well as mechanical properties of waterborne polyurethane (WPU), a novel phosphorus–nitrogen–silicon containing flame retardant WPU (FRWPU) was synthesized by conjugating with a cyclic phosphoramidate lateral group bearing diol (named as PNMPD) and silane coupling agent KH-602 in the chain-extension and post-chain extension process, respectively. Significant enhancement in tensile strength (6.1 MPa) is obtained with the combined covalent incorporation of PNMPD and KH-602 rather than using PNMPD alone. A limiting oxygen index (LOI) value of 27.7% and a UL-94 vertical burning V-0 rating is achieved for FRWPU-12.6 with 12 wt% PNMPD and 60% post-chain extension ratio by KH-602, while the peak heat release rate (PHRR), total heat release (THR), peak smoke produce rate (SPR) and total smoke production (TSP) characterized by a cone calorimeter (CC) markedly reduce by 36.0%, 42.9%, 40.1% and 35.4%, respectively, compared to those of pure WPU, which is more efficient in flame retardancy than FRWPU-12.0 merely loaded with 12 wt% PNMPD. Meanwhile, the thermal degradation behaviors and flame-retardant mechanism of FRWPU were consistently confirmed by thermogravimetric analysis (TGA), scanning electron microscopy (SEM), thermogravimetry-Fourier transform infrared (TG-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. All results indicate that the interactions between phosphorus and silicon elements in the condensed phase are mainly responsible for the dramatically reduced fire hazards, which inhibits the heat and flammable gas release and facilitates the formation of a more thermally stable graphitized char layer consisting of –P(O)–O–Si– structures.

Effect of surface free energy and wettability on the adhesion property of waterborne polyurethane adhesive

According to van Oss–Chaudhury–Goods theory, some key adhesion parameters (involving surface free energy, interfacial free energy, adhesion energy, and the spreading coefficient, etc.) of waterborne polyurethane (WPU) adhesives on shoe substrates, styrene–butadiene–styrene rubber (SBS), ethylene vinyl acetate (EVA), and polyvinyl chloride (PVC) were calculated and the relationships among the surface free energy, interfacial free energy, wettability, and adhesion property of WPU adhesives to these substrates were investigated in detail. The results indicate that the surface free energy of the substrates is the dominant parameter to influence the wettability and adhesion strength, while wetting agents can efficiently improve the wettability via decreasing the surface free energy (γL) of the adhesive, although it cannot noticeably alter the adhesion strength. Further analysis found that surface modifications, such as plasma and halogenation treatments, can introduce some active groups (–OH, –NH, or –Cl) onto the surface of SBS, which increases the surface polarity of SBS and enhances the interfacial interaction and adhesion strength of the WPU adhesives, especially in the presence of an isocyanate-terminated hardener.

A photochromic long persistent luminescent polyurethane based on a colour conversion process

A photochromic long persistent luminescent polyurethane (PLPLPU) is prepared via incorporating amino-functionalized phosphors (NH2-SrAl2O4:Eu2+,Dy3+) and the red fluorescer 1-[(2-hydrocyethly)amino]anthraquinone (HAA) based on a colour conversion process. X-ray Diffraction (XRD), UV-vis absorption spectroscopy (UV), thermogravimetric analysis (TG), a fluorescence spectrophotometer and an afterglow brightness tester as well as the percentage of the migration test were utilized to characterize the structure and properties of the resultant samples. The photoluminescence emission spectrum of phosphors is overlapped with the excitation spectrum of HAA, which demonstrates that HAA can be selected as a colour conversion agent and can be excited by phosphors in the dark. PLPLPU shows red emission in daylight and yellow in the dark, exhibiting a pleasant photochromic long persistent luminescence effect. Furthermore, HAA in PLPLPU was confirmed to have a better thermal migration stability than the blend samples due to the chemical combination.

Surfactant-assisted hydrothermal synthesis of rGO/SnIn4S8 nanosheets and their application in complete removal of Cr(VI)

To solve the problem of contamination of hexavalent chromium (Cr(VI)), visible-light-driven graphene-based ternary metal chalcogenide nanosheets (rGO/SnIn4S8) were synthesized via a one-pot surfactant-assisted hydrothermal method for the photoreduction of Cr(VI). Characterizations demonstrated that SnIn4S8 nanosheets were uniformly distributed on the surface of rGO and the as-synthesized nanosheets exhibited excellent photocatalytic activity under visible light. In addition, the effects of pH, concentration of critic acid, holes and electron scavengers on the reduction of Cr(VI) were systematically investigated. It was found that 50 mg L−1 of Cr(VI) could be completely removed within 30 min at pH 2 when citric acid served as a hole scavenger. Kinetic studies showed that the photocatalytic reduction of Cr(VI) processes obeyed the pseudo first order model. Further study indicated that the Cr(III) species was immediately adsorbed onto the surface of the rGO/SnIn4S8 nanosheets after photocatalytic reduction of Cr(VI). Additionally, recycling results suggested that rGO/SnIn4S8 nanosheets possessed high recycle ability and stability after repeated use (5 times). This effective and promising work might provide a new strategy for the photoreduction of Cr(VI) and complete removal of chromium from effluent through the novel photocatalyst rGO/SnIn4S8.

Sulfonated poly(styrene-divinylbenzene-glycidyl methacrylate)-capsulated magnetite nanoparticles as a recyclable catalyst for one-step biodiesel production from high free fatty acid-containing feedstocks

The decrease in fossil fuel resources and the negative environmental impact of greenhouse gas emissions from their combustion have stimulated interest in finding alternative energy resources. Of various alternatives, biodiesel is surging in popularity given its renewability and lower environmental impact. Herein, magnetite nanoparticles were prepared by a chemical co-precipitation technique, and then capsulated with a sulfonated poly(styrene-divinylbenzene-glycidyl methacrylate) copolymer, yielding a recyclable catalyst suitable for biodiesel production from high free fatty acid-containing feedstocks, such as waste or recycled oil. The morphology and structure of the resultant catalyst were characterized by multiple techniques, and the influence of catalyst dose, temperature, molar ratio of methanol to feedstock oil, and free fatty acid content on the biodiesel yield was evaluated, respectively. The results indicated that this catalyst was capable of catalyzing the transesterification of triglycerides and the esterification of free fatty acids simultaneously, enabling a simple, one-step procedure for biodiesel production from feedstocks containing a high content of free fatty acids. Under the optimal conditions, the biodiesel yield was found to reach 91.1%. In addition, such a catalyst was proved to be easily recyclable under an external magnetic field, and reusable, which promised its potential application in the environmentally-benign production of biodiesel from cheap waste or recycled oil.

A thermochromic luminous polyurethane based on long persistent luminescent phosphors and thermochromic pigment

A thermochromic luminous polyurethane (TLPU), which can reversibly change its color and can exhibit fluorescence emission with the change in temperature, was prepared through incorporating long persistent luminescent phosphors (SrAl2O4:Eu2+,Dy3+) and thermochromic pigment (TP). X-Ray Diffraction (XRD) patterns, differential scanning calorimetry (DSC) curves, thermogravimetic analysis results (TG), UV-vis absorption spectra (UV), reflectance spectra and fluorescence spectra were obtained to characterize the properties of the resultant samples. The phosphorescence colors were directly related to the temperature because of the inner phase transition of the thermochromic pigment on heating. TLPU was red in daylight under low temperature conditions and turned white as the temperature rose. After the stoppage of excitation and in the dark, it emitted yellow light while cooling and turned green as the temperature increased.

Synthesis and Application of Phosphorus-containing Flame Retardant Plasticizer for Polyvinyl Chloride

A novel phosphorus-containing flame retardant plasticizer (PFRP) derived from castor oil acid methyl ester (COME) was synthesized to substitute dioctyl phthalate (DOP) for plasticizing polyvinyl chloride (PVC) products. The chemical structures of PFRP were confirmed by fourier transform infrared spectroscopy (FTIR) and 1H nuclear magnetic resonance (1H NMR). Meanwhile, the plasticizing effect, flammability and thermal stability of plasticized PVC films were investigated by dynamic mechanical analyzer (DMA), limiting oxygen index (LOI) test, scanning electron microscope (SEM) and thermogravimetric analysis (TGA). As the PFRP content increasing from 0 wt% to 50 wt% amount of plasticizers, the plasticizing efficiency and the mechanical properties showed a slightly decreasing tendency compared with that of DOP, while the LOI value of plasticized PVC increased remarkably from 21.5 % to 25.2 %, showing a combined plasticizing efficiency and flame retardancy. SEM and TGA analysis indicated that PFRP had little effect on thermal stability but was effective to promote the formation of compact carbon residue.