Precursor Pretreatment Research Articles

Pre-treated municipal solid waste bottom ash as alkali-activated mortar precursor

Pre-treated incinerator bottom ash was used as a precursor of alkali-activated mortars. Control mortars were produced using coal fly ash. Different combinations of alkaline activator were tested (sodium oxide/binder ratio (4%, 6%, 8%, 10% and 15%) and silicon dioxide/sodium oxide ratio (0, 0.5, 1.0, 1.5 and 2.0)) and the influence of these on the mortar's mechanical performance was evaluated. The mortars were tested in both fresh (for density and workability) and hardened states (for dry density, compressive and flexural strengths and modulus of elasticity) after 7, 28, 91 and 182 days. The first stage of work was precursor pre-treatment in a sodium hydroxide solution to prevent the expansion of fresh specimens due to the reaction of aluminium with the alkaline activator. The pre-treatment was effective in preventing excessive hydrogen gas generation during setting, leading to dimensional stability and improved strength. Different optimum sodium oxide contents were observed after 28 days (i.e. 15% for fly ash specimens and 8% for bottom ash specimens). The results of a simplified life-cycle assessment showed that such mixes exhibited lower overall carbon dioxide emissions when compared with cement-based counterparts. However, this trend was reversed with increasing contents of sodium hydroxide and sodium silicate.

Atomic layer deposition of SnS2 film on a precursor pre-treated substrate

Two-dimensional (2D) materials are attracting attention because of their outstanding physical, chemical, and electrical properties for applications of various future devices such as back-end-of-line field effect transistor (BEOL FET). Among many 2D materials, tin disulfide (SnS2) material is advantageous for low temperature process due to low melting point that can be used for flexible devices and back-end-of-line (BEOL) devices that require low processing temperature. However, low temperature synthesis method has a poor crystallinity for applying to various semiconductor industries. Hence, many studies of improving crystallinity of tin disulfide film are studied for enhancing the quality of film. In this work, we propose a precursor multi-dosing method before deposition of SnS2. This precursor pre-treatment was conducted by atomic layer deposition cycles for more adsorption of precursors to the substrate before deposition. The film quality was analyzed by x-ray diffraction, Raman, transmission electron microscopy, atomic force microscopy and x-ray photoelectron spectroscopy. As a result, more adsorbates by precursor pre-treatment induce higher growth rate and better crystallinity of film.

Fe-enriched two-phase multiferroic composites based on lead ferroniobate - titanate and modified nickel ferrite

Iron-enriched ferroelectrics are of particular interest as piezoactive components of piezoelectric-ferrite ME ceramics. This is due to the phase composition similarity and the reduction of expected interfacial doping effects during high-temperature calcination. This idea seems attractive, but laborious due to the significantly limited number of possible piezoelectric–ferrite combinations. Therefore, there is practically no data on such systems in the literature. ME composite ceramics based on the highly efficient Fe-containing Pb(Fe0.5Nb0.5)0.935Ti0.065O3 (PFNPT) ferroelectric has been studied. (100-х) wt.% Pb(Fe0.5Nb0.5)0.935Ti0.065O3 (PFNPT) + х wt.% Ni0.9Co0.1Cu0.1Fe1.9O4-d (NCCF) composite systems has been obtained by the solid-state method at 1050 °C, with no foreign phases. The specimens densities amounted to ∼80% of the theoretical. It has been shown that the ME conversion efficiency and other composites properties are significantly influenced by the PFNPT precursor pre-treatment method. The maximum value of the ME coefficient ΔΕ/ΔΗ = 75 mV/(cm Oe) has been observed for specimens with x = 50–60 made from PFNPT powder with the addition of Li2CO3. An increase in the ME composites sintering temperature to 1150 °C leads to the formation of Pb2Nb2O7 foreign phase with a pyrochlore structure along the grain boundaries. The ME coefficient ΔΕ/ΔΗ does not exceed 15 mV/(cm⋅Oe). There is an threefold decrease in the composites piezoelectric parameters (piezoelectric coefficients dij, gij), as well as in their magnetic properties (magnetizations MS, MR) due to piezophase degradation, which is presumably associated with a change in the cations distribution over A and B sublattices of the spinel structure.

Pretreatment strategies of precursors for efficient photocatalytic hydrogen production of graphitic phase carbon nitride

The most sustainable preparation method for nanostructured materials must be urgently determined. In particular, the influence of different precursor pretreatment strategies on the structure and photocatalytic performance of highly attractive Graphitic carbon nitride photocatalyst is necessary to determine the most effective precursor pretreatment strategy. In this paper, three different precursor pretreatment methods were used to prepare g-C3N4 materials, so namely direct mixing (CN-C), freeze-drying, hydrothermal (CN-H) with thermal condensation polymerization two-step method processed urea, melamine and NH4Cl precursor mixtures. The results showed that NH4Cl, as a template, would not destroy the integrity of the tristriazine structural units in the product, and the CN-H sample had a lamellar structure, and the specific surface area and pore volume of the sample increased, which could provide more active reaction sites for photocatalytic H2 production, had the highest and most stable H2 evolution rate, up to 118.4 μmol g−1, about 1.7 times CN-C’s. This strategy provides a new idea for the design of g-C3N4 photocatalyst.

UV light-induced oxygen doping in graphitic carbon nitride with suppressed deep trapping for enhancement in CO2 photoreduction activity

• Oxygen (O) element is introduced in the bulk graphitic carbon nitride (CN) for the first time through a precursor pretreatment by ultraviolet (UV) light irradiation. • The doped O non-metal photocatalyst of CN increased visible light absorption and enhanced carrier density. • The optimized sample has lower charge recombination and suppressed electron deep trapping. • The optimized sample shows enhanced photoreduction activity of CO2 to CH4. While photoreduction of CO 2 to CH 4 is an effective means of producing value-added fuels, common photocatalysts have poor activity and low selectivity in photocatalytic CO 2 -reduction processes. Even though creating defects is an effective photocatalyst fabrication route to improve photocatalytic activity, there are some challenges with the facile photocatalyst synthesis method. In this work, an O element is introduced into a graphitic carbon nitride (CN) skeleton through a precursory ultraviolet light irradiation pretreatment to increase the visible light absorption and enhance the carrier density of this modified non-metal CN photocatalyst; the charge transfer dynamics thereof are also studied through electrochemical tests, photoluminescence spectroscopy, and nanosecond transient absorption. We verify that the optimized sample exhibits lower charge recombination and a suppressed 84 ns electron-trapping lifetime, compared to the 103 ns electron-trapping lifetime of the CN counterpart, and thereby contributes to robust detrapping and a fast transfer of active electrons. Through density functional theory calculations, we find that the improved light absorption and increased electron density are ascribed to O-element doping, which enhances the CO 2 adsorption energy and improves the CO 2 -to-CH 4 photoreduction activity; it becomes 17 times higher than that of the bare CN, and the selectivity is 3.8 times higher than that of CN. Moreover, the optimized sample demonstrates excellent cyclic stability in a 24-hour cycle test.

Optimizing dicyandiamide pretreatment conditions for enhanced structure and electronic properties of polymeric graphitic carbon nitride

The impact of dicyandiamide (DCDA) precursor pretreatment prior to thermal polymerization to graphitic carbon nitride was investigated. Pretreated samples rendered the same product yield, diverse morphologies and reduced electrochemical resistance.

Highly crystalline carbon nitride with small-sized sea urchin-like structure for efficient photocatalytic hydrogen production under visible-light irradiation

Molten-salt method has been deemed as a feasible strategy to increase the crystallinity of graphitic carbon nitride (abbreviated as CN), thereby improving its photocatalytic activity. However, highly crystalline CN prepared by molten-salt method using bulk carbon nitride (BCN) as the precursor still suffers from a small specific surface area, which is unfavorable to the separation of photogenerated carriers. Here, we report a facile approach to obtain highly crystalline CN with a large specific surface area using tubular carbon nitride (TCN) as raw material, and the final sample is named as tubular carbon nitride-molten salt (TCN-M). Compared with bulk carbon nitride-molten salt (BCN-M) sample, the obtained TCN-M sample not only retains the advantage of high crystallinity, but also exhibits a smaller-sized sea urchin-like structure owing to the CN precursor pretreatment process. The experiment results demonstrate that TCN-M displays an excellent hydrogen production activity of 4.9 mmol g -1 h -1 under visible-light, and its hydrogen production performance can be further enhanced to 14.7 mmol g -1 h -1 after adding 0.5 M K 2 HPO 4 . Thus, this work may supply valuable ideas to further optimize the photocatalytic activity of highly crystalline CN prepared by molten-salt method from the perspective of CN precursor pretreatment. • A highly crystalline carbon nitride with small-sized sea urchin-like structure was successfully prepared. • Large specific surface area and the presence of cyano groups greatly improve the photocatalytic H 2 production activity. • Optimizing the photocatalytic activity of highly crystalline CN from the perspective of CN precursor pretreatment. • A typical H + -reduction cycle can be constructed by introducing K 2 HPO 4 into the reaction system.

Porous Nitrogen-Defected Carbon Nitride Derived from A Precursor Pretreatment Strategy for Efficient Photocatalytic Degradation and Hydrogen Evolution.

Graphitic carbon nitride (g-C3N4) has attracted extensive research attention because of its virtues of a metal-free nature, feasible synthesis, and excellent properties. However, the low specific surface area and mediocre charge separation dramatically limit the practical applications of g-C3N4. Herein, porous nitrogen defective g-C3N4 (PDCN) was successfully fabricated by the integration of urea-assisted supramolecular assembly with the polymerization process. Advanced characterization results suggested that PDCN exhibited a much larger specific surface area and dramatically improved charge separation compared to bulk g-C3N4, leading to the formation of more active sites and the improvement in mass transfer. The synthesized PDCN rendered a 16-fold increase in photocatalytic tetracycline degradation efficiency compared to g-C3N4. Additionally, the hydrogen evolution rate of PDCN was 10.2 times higher than that of g-C3N4. Meanwhile, the quenching experiments and electron spin resonance (ESR) spectra suggested that the superoxide radicals and holes are the predominant reactive species for the photocatalytic degradation process. This study may inspire the new construction design of efficient g-C3N4-based visible-light photocatalysts.

A facile method for preparing porous g–C3N4 nanosheets with efficient photocatalytic activity under visible light

g–C3N4 nanosheets with porous structures (labelled PGN) were prepared by an extremely facile one-step, template-free method. The method used to prepare porous g–C3N4 nanosheets in this research was thermal polycondensation of urea pre-treated with ethanol. These nanosheets were compared with g–C3N4 agglomerates (labelled BG) prepared with raw urea. The pre-treatment process did not change the crystal structure of urea but changed the thermal polymerization process of urea to form g–C3N4. The change in the thermal polymerization process resulted in the formation of porous g–C3N4 nanosheets. The as-prepared PGN photocatalyst has an enlarged surface area of 66.0 m2 g−1 and a pore volume of 0.357 cm3 g−1, leading to enhanced visible light photocatalytic efficiency. The photocatalytic activity of g–C3N4 was evaluated by the photodegradation experiments with methylene blue (MB). The results indicated that PGN exhibited high and stable photocatalytic activity. The effective separation and transmission of photogenerated electron–hole pairs caused by precursor (urea) pre-treatment as well as the large BET surface area are associated with the enhanced photocatalytic activity of PGN.

A review of the application of carbon-based membranes to hydrogen separation

Hydrogen (H2) is a green clean fuel and chemical feedstock. Its separation and purification from H2-containing mixtures is the key step in the production of H2 with high purity (> 99.99%). Carbon membranes emerged in the 70 s and have provided promising results for applications in processes involving gas separation due to their sieving effects. Particularly, in this review, a general concept route of precursor selection-preparation-modification-performance analysis platform for the carbon membrane has been proposed to promote the development of carbon membrane material for a wide range of application. Several main parts are highlighted which are carbon membrane preparation, precursor selection, precursor pre-treatment covering pyrolysis process, carbonized membrane, pos-treatment and as well as module fabrication in order to improve the separation capability of gas mixtures in respect to permeability and selectivity. The variables of pre-treatment, the parameters of the pyrolysis process and the conditions of the post-treatment are manipulated and implied as a chance to maximize the performance of carbon membrane separation in the coming future. This review will specify an insight into the latest researches, which is expected to offer worthy implications to academicians and industry professionals working in industrial domain for the hydrogen separation. For future perspective, carbon membranes hold significant potential and great promise for further investigation, development and application.

Effects of precursor pre-treatment on the vapor deposition of WS2 monolayers.

Transition metal oxide powders have been widely used as the growth precursors for monolayer transition metal dichalcogenides (TMDCs) in chemical vapor deposition (CVD). It has been proposed that metal oxide precursors in the gas phase undergo a two-step reaction during CVD growth, where transition metal sub-oxides are likely formed first and then the sulfurization of these sub-oxides leads to the formation of TMDCs. However, the effects of stoichiometry of transition metal oxide precursors on the growth of TMDC monolayers have not been studied yet. In this contribution, we report the critical role of the WO3 precursor pre-annealing process on the growth of WS2 monolayers. Besides, several WO3 precursors with different types of oxygen vacancies have also been prepared and investigated by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and density functional theory calculation. Among all the non-stoichiometric WO3 precursors, thermally annealed WO3 powder exhibits the highest oxygen vacancy concentration and produces WS2 monolayers with significantly improved quality in terms of lateral size, density, and crystallinity. Our comprehensive study suggests that the chemical composition of transition metal oxide precursors would be fundamentally critical for the growth of large-area and high-quality WS2 monolayers, which further pave the way for revealing their intrinsic properties and unique applications.

Synthesis g-C3N4 of high specific surface area by precursor pretreatment strategy with SBA-15 as a template and their photocatalytic activity toward degradation of rhodamine B

Using SBA-15 as a template, high surface area porous graphitic carbon nitrides (g-C3N4) were successfully synthesized by pretreating melamine using hydrochloric acid, and fully characterized by Fourier-Transform infrared (FT-IR), X-ray diffraction (XRD), scanning electron micrographs (SEM), N2 adsorption-desorption, ultraviolet-visible (UV-Vis) spectroscopy, photoluminescence (PL) spectrum. The results of these analyses indicated that the g-C3N4 synthesized from HCl-pretreated melamine with SBA-15 as a template has enhanced specific surface area and increased the separation rate of the photogenerated electrons and holes compared with bulk g-C3N4, but didn’t change the structure of bulk g-C3N4. The photocatalytic activity of samples was evaluated by the degradation of rhodamine B (RhB) under xenon lamp. The results indicated that the activity was improved significantly with the increase of specific surface area. The rate constant for CN-3（HCl pretreatment melamine precursor and SBA-15 as a template） was 13 times as high as g-C3N4. Furthermore, the CN-3 catalyst exhibited outstanding structural and catalytic stability.

Facile urea-assisted precursor pre-treatment to fabricate porous g-C3N4 nanosheets for remarkably enhanced visible-light-driven hydrogen evolution

Hydrogen generation photocatalyzed by low-cost graphite carbon nitride (g-C3N4) is a fascinating and effective route to solve energy crisis, but is mainly limited by the few reactive sites, low carrier separation efficiency and mediocre visible-light utilization. In this work, these limitations were tackled through a facile eco-friendly precursor pretreatment by tuning bulk g-C3N4 into porous structure. This pretreatment restricted agglomeration in the subsequent condensation and created more porous channels for charge carrier transfer and more surface active sites for reaction. The modified g-C3N4 has larger surface area, broader visible-light response, enhanced electron migration capacity and prolonged lifetime of photogenerated carriers. These well-amended g-C3N4 nanosheets possess an average hydrogen evolution rate 5.7 times that of bulk g-C3N4. This work affords a facile, eco-friendly and scalable strategy to design or synthesize other porous materials.

Fabrication of porous g-C3N4 and supported porous g-C3N4 by a simple precursor pretreatment strategy and their efficient visible-light photocatalytic activity

Porous g-C3N4 and supported porous g-C3N4 were fabricated for the first time by a simple strategy using pretreated melamine as a raw material and pretreated quartz rod as a substrate. The formation of a richly porous microstructure can be attributed to the co-existence of different pore-fabricating units in the preparation system for porous g-C3N4. The richly porous microstructure endowed the as-prepared porous g-C3N4 with an excellent photocatalytic activity. The as-prepared supported porous g-C3N4 exhibited considerable stability because of the existence of chemical interaction between porous g-C3N4 and the quartz rod substrate. The photocatalytic activity of the supported porous g-C3N4 was competitive with that of porous g-C3N4 in powder form because neither the surface migration of photogenerated electrons nor the diffusion of the target organic pollutant were affected by the construction of the quartz rod reactor. The photocatalytic activity of the as-prepared porous g-C3N4 and supported porous g-C3N4 was preliminarily evaluated by the treatment of single-component organic wastewater under visible-light irradiation. Subsequently, the as-prepared porous g-C3N4 was further applied in conventional hydrogen evolution and a new system for simultaneous hydrogen evolution with organic-pollutant degradation. The hydrogen yield and degradation efficiency both increased with increasing photocatalytic activity of the as-prepared materials in the system for simultaneous hydrogen evolution with organic-pollutant degradation.

A new approach to improve the electrochemical performance of Li-rich cathode material by precursor pretreatment

The layered Li-rich 0.5Li2MnO3·0.5LiNi1/3Mn1/3Co1/3O2 cathode material was synthesized via a co-precipitation method. The carbonate precursor was pretreated in the mother liquor for various time and the effects on the electrochemical performance were studied. Field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD) were used to characterize the micromorphology and structure of the material. Meanwhile, charge-discharge test and electrochemical impedance spectroscopy (EIS) were employed to study its electrochemical performance. It was found that an extended precursor pretreatment time can result in relatively excellent hexagonal ordering structure and low degree of cation mixing. The material synthesized by the precursor aged in mother liquid for 12 h possessed excellent electrochemical performance. The initial discharge capacity was 262.7 mAh g−1 with the coulombic efficiency of 82.1% at 0.1 C. And the capacity retention after 50 cycles at 1.0 C was 76.9%. EIS test showed that the material had the lowest charge transfer resistance (32.02 Ω) and highest diffusion coefficientsDLi+(3.45 × 10−14 cm2 s−1).

Fabrication of b-oriented MFI Film via Langmuir-Blodgett Technique

A compact and highly b-oriented MFI-type zeolite monolayer was fabricated by assembling anisotropic zeolite micro-crystals extending over the centimeter scale by Langmuir–Blodgett (LB) method. The LB monolayer was subsequently employed as a seed layer for the secondary growth of highly b-oriented and defect-free MFI zeolite films. Firstly, LB technique was used to assemble a highly b-oriented MFI type zeolite monolayer on stainless steel substrates and platinum electrodes at an optimum target pressure of 20 mN/m constantly. Secondly, the precursor pretreatment method for preparing highly b-oriented MFI films was proved to be achievable. The crystal intergrowth and orientation of the MFI films were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The experimental results confirmed that the precursor pretreatment method was an effective route to suppress the undesired a-oriented twin growth during the secondary growth step. Finally, the highly b-oriented MFI-type zeolite film modified platinum electrodes were further tested as the working electrodes in an aqueous solution including [Fe(CN)6] with a diameter of 0.72 nm. Cyclic voltammetry experimental results demonstrated that the b-oriented MFI films fabricated by the Langmuir-Blodgett method were defect-free.

Metal organic vapor phase epitaxy of hexagonal Ge–Sb–Te (GST)

Epitaxial, hexagonal Ge–Sb–Te was grown on Si(111) substrates by Metal Organic Vapor Phase Epitaxy (MOVPE) using the precursor digermane. The effect of reactor pressure, growth temperature and in situ pre-treatment on morphology and Ge–Sb–Te composition was studied. The composition is sensitive to reactor pressure and growth temperature. Compositional control is achieved at a reactor pressure of 50hPa. Substrate pre-treatment affects film coalescence. The use of hydrogen and a suitable precursor pre-treatment leads to enhanced surface coverage. X-ray diffraction reveals a trigonal structure with lattice parameters close to that reported for Ge1Sb2Te4 crystallizing in the R3¯m phase. The composition was confirmed by energy-dispersive X-ray spectroscopy.

Carbon nitride with simultaneous porous network and O-doping for efficient solar-energy-driven hydrogen evolution

Efficient charge separation and broaden light absorption are of crucial importance for solar-driven hydrogen evolution reaction (HER), and graphitic carbon nitride (g-C3N4) is a very promising photocatalyst for this reaction. Here we report a facile precursor pre-treatment method, by forming hydrogen bond-induced supramolecular aggregates, to fabricate g-C3N4 with simultaneous novel porous network and controllable O-doping. Experimental and DFT computation identified that O doping preferentially occurs on two-coordinated N position, and the porous network and O-doping synergetically promote the light harvesting and charge separation. As a result, this material shows 6.1 and 3.1 times higher HER activity (with apparent quantum efficiency of 7.8% at 420nm) than bulk and even 3D porous g-C3N4. This work highlights that simply pre-treating the precursor can not only control the architecture but also introduce helpful foreign atoms or monomer in the matrix, which provides a useful strategy to design and fabricate highly efficient g-C3N4 photocatalyst.

Effect of surface pretreatment in the thermal atomic layer deposition of Al2O3 for passivation of crystal Si solar cells

H2O or NH4OH (5%) precursor pretreatment in the chamber was carried out before the thermal atomic layer deposition (ALD) of an Al2O3 passivation layer on p-type crystal Si. It was found that the density of negative oxide fixed charges significantly increased, the Al–O combination at the interface changed, the Al/O atomic at the interface of Al2O3/Si decreased, and the effective lifetime increased. The pretreated samples with changes in the Al–O structure at the interface, which made the interface more oxygen-rich, were believed to be the reason for the improvement of the field effect passivation in Al2O3 passivated crystal Si solar cell applications.

EASY SYNTHESIS OFLi4Ti5O12/CMICROSPHERES CONTAINING NANOPARTICLES AS ANODE MATERIAL FOR HIGH-RATELi-ION BATTERIES

A microspherical Li4Ti5O12/ C composite composed of interconnected nanoparticles with BP-2000 carbon black as carbon source is synthesized for use as an anode material in high-power lithium-ion batteries. The composite is prepared through precursor pretreatment including pre-sintering, ball-milling, and spray-drying. The structure, size and surface morphology of the as-prepared particles are investigated by X-ray diffraction and scanning electron microscopy. Results show that the obtained material has a microspherical morphology consisting of nanosized prime particles with compact structure. The precursor pretreatment effectively reduced the agglomeration of the prime particles caused by high temperature sintering and led to a more uniform distribution of BP-2000 on the surface of prime particles generating highly efficient conductive network. The specific capacity of the electrode at 20 C rate is 131 mAh g-1and the loss of capacity is less than 2% after the 60 variation cycles (from 1 C to 20 C and back to 1 C). This excellent performance is attributed to the effective conductive network between the prime particles and the reduction of the lithium-ion diffusion pathway.