Chemical Conversion Method Research Articles

Photocatalytic co-production of hydrogen gas and N-benzylidenebenzylamine over high-quality 2D layered In4/3P2Se6 nanosheets.

The concurrent photocatalytic synthesis of hydrogen gas and high-valued chemicals over two-dimensional semiconductors is extremely attractive to alleviate global energy and environmental concerns through directly using sunlight. Herein, a novel layered In4/3P2Se6 nanosheet is synthesized by a space confined chemical vapor conversion method, and it acts as a dual-functional photocatalyst to deliver the co-production of hydrogen gas and N-benzylidenebenzylamine from water reduction and selective benzylamine oxidation. The simultaneous yield of hydrogen gas and N-benzylidenebenzylamine is 895 μmol g-1 and 681 μmol g-1, respectively, within 16-hour continuous reaction involving a small amount of water in acetonitrile solvent. Moreover, 97.4% N-benzylidenebenzylamine selectivity from benzylamine oxidation can be achieved with continuous 10 hour-reaction only in acetonitrile solvent under ambient conditions. Further in situ electron paramagnetic resonance measurements and reaction optimization tests reveal that the reaction mechanism strongly relies on the conditions over the In4/3P2Se6 nanosheet photocatalyst.

Defect engineering to boost catalytic activity of Beta zeolite on low-density polyethylene cracking

Catalytic cracking is of considerable interest as a sustainable, renewable, efficient, and eco-friendly chemical conversion method of plastic wastes. In catalytic cracking, plastic wastes can be converted into valuable products such as monomers or petrochemical feedstock. Solid acid catalysts, especially zeolites, significantly lower the thermal decomposition temperature of plastics. However, the catalysts have not shown enough performance to be implemented in society. Therefore, major efforts have recently been devoted to solving this problem by appropriately designing zeolite catalysts. Herein, we report a new defect-rich Beta zeolite synthesized by a dry gel conversion method using methyltriethoxysilane. The obtained catalyst exhibited outstanding activity on low-density polyethylene cracking. We measured Fourier-transform infrared spectra using pyridine as a probe molecule and found that this high activity is contributed by the increase of the amount of Lewis acid sites. It probably arises from the ratios of extra-framework hexacoordinated aluminum and silanol groups higher than the conventional Beta zeolite shown in 27Al and 1H magic angle spinning nuclear magnetic resonance spectra. We can say that the increase of defects of zeolite Beta further accelerated polymer cracking. This work provides a new strategy to improve the catalytic activity of zeolites on polymer cracking.

From Adsorbent to Photocatalyst: The Sensitization Effect of SnO2 Surface towards Dye Photodecomposition.

Semiconductor photocatalysis is considered one of the most promising technologies for water purification from toxic organic dyes. However, to reliably evaluate the possibility of using a given material as a photocatalyst, it is crucial to investigate not only the photocatalytic activity but also its affinity towards various dyes and reusability. In this work, we studied the adsorptive/photocatalytic properties of hollow-spherical raspberry-like SnO2 and its SnO2/SnS2 heterostructures that were obtained via a chemical conversion method using three different concentrations of a sulfide precursor (thioacetamide). The adsorptive/photocatalytic properties of the samples towards cationic rhodamine B (RhB) and anionic indigo carmine (IC) were analyzed using uncommon wall zeta potential measurements, hydrodynamic diameter studies, and adsorption/photodecomposition tests. Moreover, after conducting cyclic experiments, we investigated the (micro)structural changes of the reused photocatalysts by scanning electron microscopy and Fourier-transform infrared spectroscopy. The obtained results revealed that the sensitization of SnO2 resulted not only in the significantly enhanced photocatalytic performance of the heterostructures, but also completely changed their affinity towards dyes. Furthermore, despite the seemingly best photocatalytic performance, the sample with the highest SnS2 content was unstable due to its (micro)structure. This work demonstrates that dye adsorption/desorption processes may overlap the results of cyclic photodecomposition kinetics.

Methods for chemical conversion of plastic wastes into fuels and chemicals. A review

Methods for chemical conversion of plastic wastes into fuels and chemicals. A review

Stabilization of Zn Metal Anode through Surface Reconstruction of a Cerium‐Based Conversion Film

AbstractCorrosion and dendritic deposition have been the long‐standing interfacial challenges of Zn anode, resulting in the deterioration of the aqueous zinc‐based batteries. Herein, the surface of Zn metal anode is pioneeringly reconstructed by a cerium‐based conversion film (Zn@CCF) through a chemical conversion method. Faster growth of the film in the vicinity of zinc grain boundaries significantly prevents the substrate from genetic micro‐corrosion that leads to catastrophic damage. The affinity of the film toward zinc facilitates a low nucleation barrier and smooth zinc deposition. Consequently, Zn@CCF enables long‐term lifespan (1200 h) with low polarization (≈60 mV) at 4.4 mA cm−2, which also maintains good capacity retention and excellent cycling stability of Zn@CCF/MnO2 full cells. This facile and effective approach helps suppress Zn dendrite formation and brings forward the significance of surface reconstruction of the Zn metal anode for corrosion inhibition, which can be potentially applied to other metal anodes in aqueous energy storage systems.

Fabrication of superhydrophobic needle-like Ca-P coating with anti-fouling and anti-corrosion properties on AZ31 magnesium alloy

The poor corrosion resistance of magnesium (Mg) alloys limits their applications, and preparing the superhydrophobic coating with a facile and cost-effective method is meaningful for anti-corrosion protection of Mg alloys. In this work, a superhydrophobic needle-like Ca-P coating was fabricated on AZ31 substrate by a chemical conversion method and low energy modification with stearic acid. The water contact angle of the obtained coating was about 158.7° and the sliding angle was 1.5°. Due to the stable superhydrophobicity and durability of the coating, it can not only resist the pollution of muddy water and particulate contaminants, but also withstand the destruction of high temperature and external mechanical force. And the anti-fouling ability of the coating was evaluated from the force model of the contamination. In addition, the electrochemical measurements indicated that the superhydrophobic sample exhibited excellent anti-corrosion performance in Hank's solution, and the coating could behave as the protective barrier to the substrate. Therefore, the anti-fouling, robust and corrosion-resistant superhydrophobic coating has significant advantages in the protection of Mg alloys.

Fabrication and properties of the superhydrophobic ceria‐based composite coating on magnesium alloy

AbstractA superhydrophobic ceria‐based composite coating is developed to improve anticorrosion properties of AZ61 magnesium alloy, fabricating via chemical conversion method followed by hydrothermal treatment. The cerium conversion coating has a block structure with microcracks. After the hydrothermal treatment, a dense CeO2 layer, porous CeO2 nanorods, and stearic absorbing layers are grown stepwise on the conversion coating. And the composite coating is hydrophobic or even superhydrophobic and has almost no microcracks. As the hydrothermal reaction time increases, the water contact angle of the composite coating first increases and then decreases, and it reaches the maximum value of 152° after hydrothermal treatment for 4 h. Both the dense CeO2 layer and the superhydrophobic stearic absorbing layer can effectively prevent the electrolyte from contacting the substrate; the corrosion current density of the superhydrophobic composite coating is lower than that of the hydrophilic composite coating and the cerium conversion coating, and has the best corrosion resistance.

Evaluation of low-cost high performance solid-state supercapacitor derived from physically and chemically activated oil palm fiber

This study is geared towards harnessing the promises of Oil Palm Fiber (OPF) as a renewable substitute for electrode material of supercapacitor. Physical and chemical activation conversion methods were used to activate OPF. The structural and physiochemical properties of the activated carbon derived from OPF were studied and analyzed using FESEM, XRD, BET, XPS, and FTIR. The electrochemical properties of supercapacitors fabricated from P_OPF and C_OPF were studied and reported using cyclic voltammetry, Galvanostatic charge discharge and electrochemical impedance spectroscopy.

Calcium phosphate coatings enhance biocompatibility and degradation resistance of magnesium alloy: Correlating in vitro and in vivo studies

Magnesium (Mg) and its alloys are promising biodegradable materials for orthopedic applications. However, one of the major problems is their rapid degradation rate with quick evolution of hydrogen gas. To overcome this problem, calcium phosphate (CaP) coatings have been used to improve the degradation resistance and the biocompatibility of Mg materials. This study focuses on the comparison and correlation of the in vitro and in vivo degradation and biocompatibility behaviors of these materials. A CaP coating consisting of dicalcium phosphate dihydrate (DCPD) was deposited on an AZ60 Mg alloy by the chemical conversion method. Then, the in vitro degradation testing including electrochemical and immersion tests, and in vivo implantation of the CaP coated Mg alloy were conducted to compare the degradation behaviors. Next, the in vitro cell behavior and in vivo bone tissue response were also compared on both uncoated and CaP-coated Mg samples. Data showed that the CaP coating provided the Mg alloy with significantly better biodegradation behavior and biocompatibility. The in vitro and in vivo biocompatibility tests exhibited good consistency while not the case for biodegradation. Results showed that the in vitro electrochemical test could be a quick screening tool for the biodegradation rate, while the in vitro immersion degradation rate was often 2–4 folds faster than the in vivo degradation rate.

Enhanced corrosion resistance and biocompatibility of biodegradable magnesium alloy modified by calcium phosphate/collagen coating

Magnesium (Mg) and its alloys have been regarded as one of the most promising biodegradable implant materials, whereas the rapid degradation rate and potential cytotoxicity hinder their clinic applications. In order to improve the biocompatibility and biocorrosion resistance of Mg alloy, a composite coating which composed of calcium phosphate (CaP) and collagen (Col) was successfully fabricated on the surface by chemical conversion and dip-coating methods. The chemical compositions, surface morphologies and corrosion resistance of the CaP/Col coating were investigated using X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), electrochemical and immersion test. Results revealed that the collagen coating efficiently sealed the cracks and pores of CaP coating, and significantly enhanced the corrosion resistance. Furthermore, the composition of the CaP/Col coating was similar to that of bone, which can more effectively promote the adhesion, proliferation and differentiation of osteoblasts, showing excellent biocompatibility and biosafety. These observations indicated that the CaP/Col coating could protect Mg alloy from fast degradation, greatly enhance biocompatibility and osteoinductivity, and thus could be promising for orthopedic implant applications.

Antibacterial activities and cytocompatibility of zinc-contained strontium phosphate coating on titanium

Periprosthetic joint infection (PJI) is one of the most pivotal issues accounting for clinical failure of titanium (Ti)-based implants. Therefore, it is of great significance to develop an antibacterial coating with high biocompatibility on the Ti implant surface. In this article, a novel zinc-doped strontium phosphate coating, denoted as Sr-Zn-PCC, was deposited on Ti substrates by phosphate chemical conversion (PCC) method. The texture characterizations indicated that continuous coatings containing SrHPO4, Sr3(PO4)2 and SrZn2(PO4)2 phases were formed on the Ti surface. It is found that the doping of Zn could tune the surface microstructure, roughness, wettability and corrosion resistance of the coatings. The Sr-Zn-PCC coating showed the same bacterial adhesion property at short time (2 h), but tended to hinder biofilm formation on coatings after incubation for up to 24 h. Up to 80% of Staphylococcus aureus (S. aureus) were killed within 24 h by contact with the Sr-Zn-PCC surface. Moreover, cytocompatibility assay indicated that MC-3T3 cells had good adhesion, spreading properties on the coatings, suggesting that it is a promising alloy with both excellent antibacterial ability and high biocompatibility for the applications on orthopedic implants.

Enhancement of corrosion resistance and biocompatibility of Mg-Nd-Zn-Zr alloy achieved with phosphate coating for vascular stent application

We have developed a convenient chemical conversion method of preparing a Mg3(PO4)2 coating with a lamellar structure of about 1–5μm width on Mg-Nd-Zn-Zr (denoted as JDBM) alloy, aiming to improve the corrosion resistance and biological response. The protective effect of the phosphate coating on JDBM alloy leads to an increase in corrosion resistance of about 25% from 0.337±0.021 to 0.253±0.047mmy−1. A systematic study on in vitro cytocompatibility test shows that the phosphate coated JDBM has minimal negative effect on human umbilical vein endothelial cells (HUVECs) viability, growth and proliferation, and the coating also presents a favorable affinity for HUVECs by supporting higher adherent cell density and sufficient cell spreading. In addition, the investigation of in vitro hemocompatibility confirms reduced hemolysis ratio and excellent anti-platelet adhesion property of the phosphate coated JDBM. Furthermore, this study also presents our more recent efforts to develop an in-depth understanding of the mechanism which is involving anti-platelet adhesion on the surface of biodegradable Mg substrate.

Synergy between thermal and nonthermal effects in plasmonic photocatalysis

Plasmonic photocatalysis represents the synergetic union of two active fields of research: plasmonic effects in illuminated metallic nanoparticles and catalytic effects in tailored metallic nanoparticles. Traditionally, metallic nanoparticles that excel for one application are limited for the other, but recent developments have shown that desirable catalytic behaviors, such as reduced activation barriers and improved product selectivity, derive from nonthermal behaviors uniquely produced by this synergy. After examining such findings, this review will address a specific debate that has recently surfaced: what is the relative degree of contributions of thermal and nonthermal effects in plasmonic photocatalysis? We demonstrate the importance of correctly accounting for thermal effects before characterizing nonthermal contributions. We show that another synergy occurs: these desirable nonthermal behaviors have a temperature dependence, and the resulting temperature-dependent reaction rates far exceed what can be explained from purely thermal effects alone. Thus, the synergy of plasmonic photocatalysis offers an exciting new contribution to the quest for efficient, selective, sustainable methods for chemical synthesis and energy conversion.

Surface passivation of zinc ferrite nanorod photoanodes by spray-deposited silicon oxide layer for enhanced solar water splitting

Abstract ZnFe2O4 nanorods (NR's) were prepared by a chemical conversion method from β-FeOOH NRs grown on FTO substrates. To activate their photoactivity of ZnFe2O4 NRs for solar water splitting, the surface passivation was achieved with SiO2 layer via facile and effective spray pyrolysis method. The presence of SiO2 layer enhances the photocurrent density of the Pristine ZnFe2O4 from 143 µA/cm2 to 212 µA/cm2 at 1.23 VRHE for 0.25 mM Si–ZnFe2O4, representing two time increment in the photocurrent density. The influences of amount of Si precursor (Tetraethyl orthosilicate) solutions on the physical properties and the passivation effect of SiO2/ZnFe2O4 interfaces were investigated. This improved photoresponse of the Si-treated ZnFe2O4 NRs was attributed to the excellent charge transfer electrode/electrolyte interface. The effectively improved charge transfer properties of the Si-treated ZnFe2O4 NRs were demonstrated by the electrochemical impedance spectroscopy (EIS), Mott–Schottky (MS) and intensity-modulated photocurrent spectroscopy (IMPS) analyses.

High corrosion resistance film on rebar by cerium modification

A cerium film was prepared on the surface of rebar by chemical conversion method to enhance its corrosion resistance. The film in the simulated concrete pore solution was measured by electrochemical method, transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). The effect of temperature on film formation was studied, and the optimum temperature was determined at 35 °C. The film produced by too high formation temperature has more defects, resulting in the lower corrosion resistance. The Ce film resistance increased with time evolution until 800 h, then decreased and stabilized. The Ce film layer has a double-layer film structure, the upper layer is an oxide of cerium, and the underlayer is an oxide of iron. Results revealed that after being immersed in the simulated concrete pore solution, the corrosion resistance of the Ce film was enhanced by self-densification.

A Ti(III) reduction method for one-step conversion of seawater and freshwater nitrate into N2 O for stable isotopic analysis of 15 N/14 N, 18 O/16 O and 17 O/16 O.

The nitrogen and oxygen (δ15 N, δ18 O, and δ17 O values) isotopic compositions of nitrate (NO3 - ) are crucial tracers of nutrient nitrogen (N) sources and dynamics in aquatic systems. Current methods such as bacterial denitrification or Cd-azide reduction require laborious multi-step conversions or toxic chemicals to reduce NO3 - to N2 O for 15 N and 18 O isotopic analyses by isotope ratio mass spectrometry (IRMS). Furthermore, the 17 O composition of N2 O cannot be directly disentangled using IRMS because 17 O contributes to mass 45 (15 N). We describe a new one-step chemical conversion method that employs Ti(III) chloride to reduce nitrate to N2 O gas in septum sample vials. Sample preparation takes only a few minutes followed by a 24-h reaction producing N2 O gas (65-75% recovery) which partitions into the headspace. The N2 O headspace was measured for 15 N, 18 O and 17 O by IRMS or laser spectrometry. IRMS and laser spectrometric analyses gave accurate and reproducible N and O isotopic results down to 50 ppb (3.5 μM) NO3 -N, similar in precision to the denitrifier and Cd-azide methods. The uncertainties for dissolved nitrate reference materials (USGS32, USGS34, USGS35, IAEA-NO3 ) were ±0.2‰ for δ15 N values and ±0.3‰ for δ18 O values using IRMS. For laser-based N2 O isotope analyses the results were similar, with an δ17 O uncertainty of ±0.9‰ without any need for 15 N correction. Advantages of the Ti(III) reduction method are simplicity, low cost, and no requirement for toxic chemicals or anaerobic bacterial cultures. Minor corrections may be required to account for sample nitrate concentration variance and potential chemical interferences. The Ti(III) method is easily implemented into laboratories currently using N2 O headspace sampling apparatus. We expect that the Ti(III) method will promulgate the use of N and O isotopes of nitrate in important studies of nutrient dynamics and pollution in a wide range of aquatic ecosystems.

Corrosion Behavior of AZ91D Magnesium Alloy with a Calcium–Phosphate–Vanadium Composite Conversion Coating

A novel self-healing calcium–phosphate–vanadium (Ca–P–V) composite coating on Mg alloy was successfully fabricated through a chemical conversion method. The effects of the vanadium concentration on the anticorrosion property of the substrate were also tested. The Ca–P–V coating with the main composition of CaHPO4, Ca3(PO4)2, and Mg3(PO4)2, with some hydroxides of V(V) dispersed into it has a similar morphology to the single vanadium coating. The corrosion behaviour of the Ca–P–V coating was studied through the electrochemical tests and the scratch immersion test in 3.5 wt % NaCl solution. The results showed that the Ca–P–V coated samples not only exhibit good corrosion resistance property, but also show self-healing ability. The ions of Ca, P, and V released from the coating can migrate in the corrosion solution and form a new compound layer on the damaged zone.

Enhanced cytocompatibility and antibacterial property of zinc phosphate coating on biodegradable zinc materials

Zinc (Zn) has recently emerged as a promising biodegradable metal thanks to its critical physiological roles and promising degradation behavior. However, cytocompatibility and antibacterial property of Zn is still suboptimal, in part, due to the excessive Zn ions released during degradation. Inspired by the calcium phosphate-based minerals in natural bone tissue, zinc phosphate (ZnP) coatings were prepared on pure Zn using a chemical conversion method in this study. The coating morphology was then optimized through controlling the pH of coating solution, resulting in a homogeneous micro-/nano-ZnP coating structure. The ZnP coating significantly increased the cell viability, adhesion, and differentiation of pre-osteoblasts and vascular endothelial cells, while significantly reduced the adhesion of the platelets and E. coli. Additionally, ZnP coating significantly reduced the Zn ion release from the bulk material during degradation process, resulting in a much lower Zn2+ concentration and pH change in the surrounding environment. The improved hemocompatibility, cytocompatibility and antibacterial performance of ZnP coated Zn biomaterials could be mainly attributed to the controlled Zn ion release and micro-/nano-scaled coating structure. Taken together, ZnP coating on Zn-based biomaterial appears to be a viable approach to enhance its biocompatibility and antibacterial property as well as to control its degradation rate.Statement of SignificanceZn and its alloys are promising biodegradable implant materials for orthopedic and cardiovascular applications. However, notable cytotoxicity has been reported due to degradation products accumulated in the local environment, largely overdosed Zn2+. Thus, controlling burst Zn2+ release is the key to minimize the toxicity of Zn implants. To achieve this goal, we prepared a homogenous ZnP coating on Zn metals thanks to its easy synthesis, stable chemical property, and good biocompatibility. Results showed that ZnP not only improved the cell viability, adhesion and proliferation, but also significantly reduced the attachment of platelet and bacterial. Therefore, ZnP could be a promising approach to improve the functional performance of Zn-based implants, and potentially be applied to many other medical implants.

Blank experimental study on the determination of nitrogen and oxygen isotopes by chemical conversion method.

The reduction of nitrate to nitrous oxide by chemical conversion has the characteristics of simple operation and high sensitivity. Therefore, it is widely used in the pretreatment of nitrogen and oxygen isotopes. In this paper, a series of blank experiments were performed to determine various factors influencing the determination process for the chemical conversion method. To determine blank background values for reagents such as deionized water, NaCl and cadmium powder used in the experiment, the optimal experimental conditions of NaN3, NaCl and cadmium powder were determined to maximize the nitrate reduction rate. The results showed that NaCl was burned at 450 °C for 48 hours, and the placement time was not more than one day, which could minimize the pollution introduced by NaCl. When 0.3 g of cadmium powder and 600 nmol of NaN3 were added, the overall reduction efficiency reached 90%. After measuring actual standard samples, the method demonstrated a good accuracy and applicability.

Effect of Benzotriazole on Corrosion Resistance of Al2O3/Cerium Oxide Composite Films on the Al Surface

Al2O3/cerium oxide composite films were prepared on the surface of aluminum by an anodic oxidation and chemical conversion method. The aluminum was firstly anodized in sulfuric acid, and then the anodized aluminum was treated with the Ce(NO3)3 solution. The effect of different concentrations of 1H-Benzotriazole (BTA) on the corrosion resistance of Al2O3/cerium oxide composite films was investigated. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) with energy dispersive spectrometer (EDS), and electrochemical workstation were used to characterize the properties of the composite films. The results show that the deposition effect of cerium ions is optimal in 0.5 g/L BTA. At the same time, the surface uniformity and smoothness of the composite films are both enhanced. And the corrosion resistance of the composite film is strengthened.