Smaller Specific Surface Area Research Articles

Supramolecular Self-Assembly of g-C3N4 Nanoplatform as Drug Delivery Carriers for Cancer Therapy

Graphite carbon nitride (g-C3N[Formula: see text] polymer with two-dimensional planar structure is a new star in nanodrug delivery systems in recent years because it shows characteristics of low cost, nontoxicity, biocompatibility and easy functionalization. However, conventional g-C3N4 shows bulk, macro size, small specific surface area and poor water solubility. To improve this, most works are always confined to physical ultrasound, oxidative peeling or template-strategy, which have the disadvantages of redundant steps, environment-unfriendliness and high cost. In this paper, a modified supramolecular self-assembled strategy was carried out to construct a novel graphitic carbon nitride nanoplatform (named by CA-MA[Formula: see text] using melamine and cyanuric as precursors. The chemical structure characterization, drug loading experiment and cell tests in vitro of the CA-MA[Formula: see text] nanoplatform were carried out and discussed in detail. Results indicated that the obtained samples show enhanced specific surface area, more exposed groups and good biocompatibility. Compared to the traditional carbon nitride (named by MA-CN), the newly prepared CA-MA[Formula: see text] carrier shows improved drug loading efficiency and good pH-responsive loading, as well as releasing. Cell uptake experiment demonstrates that CA-MA2-DOX can be swallowed by cancer cells and during treatment of the cancer cell process, the CA-MA2-DOX complex experiences phagocytizing by the cancer cell, controlled-release DOX and kills the cancer cell after DOX was passively diffused into the nucleus. CA-MA2-DOX exhibited significant in vitro antitumor activity. To our knowledge, this is the first time the supramolecular self-assembled method was used in carbon nitride nanocarrier construction for cancer treatment.

Heterogeneous La and CeOx co-promoted SAPO-11 catalyst for catalytic upgrading of cellulose-derived volatile and methanol into hydrocarbon-rich fuels

In this paper, a series of La–Ce co-doped SAPO-11 catalysts with various La to Ce ratio were developed via wet impregnation method then employed in catalytic cellulose and methanol co-pyrolysis to produce hydrocarbon-rich biofuels. Comprehensive characterization technologies including X-ray diffraction, X-ray photoelectron spectroscopy, N2 physisorption, scanning electron microscope, transmission electron microscope, ammonia temperature-programmed desorption, Pyridine-infrared, and thermal gravimetric analyzer, were conducted to unveil the physicochemical properties, structure properties and acidity of as-prepared catalysts. Additionally the product content; aromatic selectivity and synergetic effect were also investigated. Additionally possible conversion pathway, deactivation mechanism and reusability were also deduced. La and Ce showed a certain synergetic effect and exhibited superior catalytic deoxygenation activity due to La–O and Ce-Ox species, suitable Brønsted acidity, abundant oxygen vacancies and enhanced mesopores structure, which was facilitated to promote the selectivity of hydrocarbon. Higher La content was fascinated to generate furans and ketones compounds, due to lower Brønsted acid site and smaller specific surface area. In contrast, higher CeOx content was beneficial to hydrocarbon formation via Diels-Alder reaction and dehydro-aromatization due to higher Brønsted acid site, total acidity, higher specific surface area, mesoporous pore volume as well as strong oxygen affinity of CeOx. The maximum proportion hydrocarbon, aromatics and minimum contents coke was obtained over 1La–1Ce/SAPO-11 were 77.96 %, 55.82 % and 9.81 %, respectively. Additionally, 1La–1Ce/SAPO-11 catalyst exhibited outstanding reusability and stability after four cycles; nearly ∼96 % relative content of hydrocarbon was maintained after regeneration test. Hence, the insight into the synergetic catalysis between La and CeOx species could provide a new potential possible pathway for design and synthesized efficient and eco-friendly bimetallic catalyst for selective catalytic deoxygenation organic solid waste biomass for valuable chemicals.

Development of sulfhydryl grafted hierarchical porous geopolymer for highly effective removal of Pb (II) from water

Geopolymers have captured increasing attention in the adsorption of lead ions due to their zeolite-like three-dimensional network structure, and several advantages such as low cost and environmental friendliness. However, their adsorption performance is limited by a small specific surface area and fewer adsorption sites. In this study, a metakaolin-based geopolymer was first pretreated with different concentrations of nitric acid to increase the porosity and surface area. Subsequently, the sulfhydryl functional group was grafted onto the above hierarchical porous geopolymer, which is a inorganic material with multistage pore structure. The result of N2 adsorption and desorption results demonstrated that an increase in specific surface area and number of grafting sites for sulfhydryl groups with increasing acid concentration when the highest nitric acid concentration used is 5 mol/L and acid treatment time is for 5 h. The specific surface area of the fabricated geopolymers was as high as 343.87 m2/g and the concentration of silanol groups reached 4.46 mmol/g at 3 mol/L acid concentration. The maximum Pb2+ adsorption quantities for SH-1HGeo, SH-2HGeo, and SH-3HGeo samples were 173.2 mg/g, 239.8 mg/g, and 386.3 mg/g, respectively. The adsorption processes were in accordance with the pseudo-second-order kinetic model and the Langmuir models, indicating that the Pb2+ adsorption on the sulfhydryl grafted hierarchical porous geopolymer was mainly chemisorption and monolayer adsorption. The contribution of different Pb2+ adsorption mechanism on geopolymer was ion-exchange, while that on SH-3HGeo was functional group complexation.

Catalytic oxidation of carbon monoxide over copper oxide with interfering gases involved for industrial buildings: An experimental and theoretical study

With the intention of thoroughly eliminating carbon monoxide (CO) from indoor environment, it is one of the most promising methods of converting it into carbon dioxide (CO2) via catalytic oxidation processes. Therefore, in this study, catalytic oxidation mechanisms of CO over copper oxide (CuO) with interfering gases involved are investigated via theoretical calculations and experimental verification, which mainly include basic catalytic oxidation processes over CuO, effects of different interfering gases and analyses of thermodynamic features. According to results, catalytic oxidation of CO over CuO can be performed in three different routes and rate-determining transition-state (TS) energy barriers vary a lot from route to route at high temperature owing to different thermal stability. In the meantime, SO2, H2O and NO are theoretically proved to affect catalytic oxidation of CO via competitive adsorption, high oxidizability and hydrogen bonds, which are accompanied with different sensitivities to changes of temperature or temperature power exponents. In experiments, it is found that impurity of lattice planes and small specific surface areas in CuO are key to restricting catalytic oxidation performances. What is more, some extra chemical reactions in experiments (e.g. SO2 + O2 + CuO → CuSO4, NO + O2 + CO → CO2 + NO) caused by interfering gases colossally affect catalytic oxidation performances of CuO. The whole study provides crucial information for indoor air purification in industrial buildings by using cheap adsorbents/catalysts.

Combined Analyses on Electronic Structure and Molecular Orbitals of d10 Bimetal Oxide In2Ge2O7 and Photocatalytic Performances for Overall Water Splitting and CO2 Reduction.

Semiconducting photocatalytic overall water splitting and CO2 reduction are possible solutions to the emerging worldwide challenges of oil shortage and continual temperature increase, and the key is to develop an efficient photocatalyst. Most photocatalysts contain the d0, d10 or d10ns2 metals, and a guiding principle is desired to help to distinguish outstanding semiconductors. Here, the d10 bimetal oxide In2Ge2O7 was selected as the target. First, density functional theory (DFT) calculations point out that the nonbonding O 2p orbitals dominate the valence band maximum (VBM), and In 5s-O 2s and Ge 4s-O 2s antibonding orbitals are the major components of conduction band minimum (CBM). Moreover, the molecular orbitals were analyzed to consolidate the DFT calculations and make it more understandable for chemists. Due to the very small specific surface area (0.51 m2/g) and wide band gap (4.14 eV), as-prepared In2Ge2O7 did not exhibit any overall water splitting activity; nevertheless, when loading with 1 wt% cocatalyst (i.e., Pt, Pd), the surficial charge recombination can be greatly eliminated and the overall water splitting activity is significantly improved to 33.0(4) and 17.2(7) μmol/h for H2 and O2 generation, respectively. The apparent quantum yield (AQY) at 254 nm is 8.28%. This observation is proof that the inherent electronic structure of In2Ge2O7 is beneficial for the charge migration in bulk. Moreover, this catalyst also exhibits an observable CO2 reduction activity in pure water, which is a competition reaction with water splitting, anyway, the CH4 selectivity can be enhanced by loading Pd. This is a successful attempt to unravel the structure-property relationship by combining the analyses on electronic structure and molecular orbitals and is enlightening to further discover good candidates to photocatalysts.

Hydrodynamics of a bubble passing through a Kelvin cell in microchannel with shear-thinning fluid

Open cell solid foams (OCSF) show great potential for process intensification in heterogeneously catalyzed reactions due to their favorable properties regarding heat-mass transfer, pressure drop and specific surface area (SSA). As one of the most ideal OCSF structure, Kelvin cell (KC) exhibits a fundamental importance in fully understanding the complex flow and transport properties of these reactions, but the research involving gas-liquid two-phase flow is still missing. In this work, the hydrodynamics of a bubble through a representative elementary volume with KC model in minichannel with sodium carboxymethyl cellulose aqueous solution are investigated by coupled level-set and volume-of-fluid method. The regime of bubble penetration into KC is elucidated. The specific surface area and permeability of bubble are studied by systematically analyzing the influences of solution concentration, liquid velocity, KC's porosity and contact angle, as well as fluid type. Four penetration regimes of approaching stage, engraving stage, extruding stage, and deviating stage are identified, and a typical curve of SSA of bubble in terms of flow time is acquired accurately. It is found that the drastic changes in SSA and permeability are closely related to the engraving and extruding stages. The average SSA in two involved stages increases with solution concentration, decreases with KC's porosity. The maximum permeability corresponding to the transition point between two stages, decreases with solution concentration, increases slightly with KC's porosity. However, liquid flow velocity and KC's contact angle have no significant effect on both the average SSA and the maximum permeability. Compared with water, a small SSA tends to be obtained and the permeability climbs slowly but reaches a high peak in CMC solution.

Effect of static magnetic field pretreatment on the structure and oil absorption properties of normal maize starch

In this work, we report the effect of static magnetic field (SMF) on normal maize starch (NMS) structure and oil absorption properties. The results showed that the untreated NMS had the total oil absorption of 83.90%, solubility of 19.00%, swelling power of 20.32 g/g, and amylose content of 26.95%. Besides, compared with untreated NMS, pretreatment with different SMF strengths significantly reduced the total oil absorption (61.78–78.12%), solubility (16.99–18.61%), swelling power (17.62–19.02 g/g), and amylose content (19.77–24.73%) of NMS. Besides, the SMF-pretreated NMS had a rough surface with more pits and pores, a denser particle structure, and a smaller specific surface area and particle size than untreated NMS. However, the high SMF intensity (50 mT) made NMS form a porous structure, leading to the highest oil absorption of NMS (78.12%), but still less than untreated NMS (83.90%). FT-IR, XRD, and DSC studies further showed that SMF pretreatment improved the structural ordering and thermal stability of NMS particles, inhibiting the oil absorption of NMS. To investigate whether SMF pretreatment could reduce starch-based fried food oil absorption, LF-NMR was used to determine the oil content of fried NMS treated with different SMF strengths. Results indicated the oil content of NMS after frying was significantly reduced by SMF pretreatment than untreated NMS, and the lowest was 0.2751 g/g for SMF-30. Therefore, SMF pretreatment can effectively reduce the oil absorption capacity of NMS before and after frying and serve as a prospective technology to reduce the oil content of starch-based fried foods.

Facile Room Temperature Synthesis of Precious‐Metal‐Free Coordination Polymer Photocatalyst for Improved Visible‐Light CO2 Reduction

The Pb–S‐based coordination polymer (CP), named KGF‐9, [Pb(tadt)]n (tadt = 1,3,4‐thiadiazole‐2,5‐dithiolate), can selectively convert CO2 into HCOO− (>99%) under visible light, with an apparent quantum yield (AQY) of 2.6% at 400 nm, without a cocatalyst. However, KGF‐9 is an intrinsically nonporous CP, and its small specific surface area (<1 m2 g−1) might hinder the realization of its full potential as a photocatalyst. Herein, facile synthetic routes at room temperature are reported through a solid‐state reaction and a liquid‐phase reaction (LPR) using lead(II) acetate as a precursor. The use of lead(II) acetate promotes the deprotonation of the H2tadt ligand, resulting in a faster coordination reaction, a reduced feature size, and a drastic increase in specific surface area (≈10 m2 g−1). A higher AQY for formate production (5.9% at 400 nm) is found for KGF‐9 prepared via a 60 min LPR. The improved photocatalytic activity of the LPR sample is attributed to the presence of long‐lived charge carriers, which is revealed by time‐resolved microwave conductivity measurements. The results of this study provide a simple but effective strategy toward increasing the activity of CP‐based photocatalysts.

Flexible Si/PEDOT:PSS heterojunction photodetectors with excellent interface contact quality for NIR detection

Flexible Si/PEDOT:PSS heterojunction photodetectors have gained widespread attention due to their excellent performance and low preparation cost, however, the presence of defects on the Si surface that generate surface states and the poor hydrophilicity of PEDOT:PSS that leads to poor contact between Si and PEDOT:PSS have been limiting the performance of the devices; In this study, an inverted pyramidal structure Si substrate with the smaller specific surface area was selected and the Si to PEDOT:PSS interface quality was improved by doping the PEDOT:PSS solution with the fluorosurfactant FC4430 and vinyltrimethoxysilane (VTMO). It was found that the doping of fluorosurfactant FC4430 could reduce the contact angle of PEDOT:PSS solution on IP substrate from 104.5° to 23°, which greatly enhanced the hydrophilicity of PEDOT:PSS without affecting the electrical properties of the films. The doping of VTMO forms Si-O-Si bonds at the Si/PEDOT:PSS interface, which passivates the defects on the silicon surface and at the same time forms a cross-linking network to improve the adhesion of the PEDOT:PSS, which enables the device to exhibit an extremely low dark current of 4.08 × 10−8 mA. Meanwhile, the prepared flexible Si/PEDOT:PSS photodetector exhibits excellent performance, with a responsivity of 8.74 mA/W, a detectivity of 1.21 × 1012 Jones, and a response speed of 120/480 μs under 0 V bias voltage and laser irradiation at a wavelength of 980 nm. Finally, the bending stability of the device was evaluated and the device performance remained above 95 % of the initial value after 50 bending cycles.

Recent Trends in Foliar Nanofertilizers: A Review.

It is estimated that 40-70%, 80-90% and 50-90% of the conventional macronutrients N, P and K applied to the soil are lost, respectively, resulting in considerable loss of resources. Compared to conventional fertilizers, nanofertilizers have the advantages of controlled release, high nutrient utilization, low cost and relatively low environmental pollution due to their small size (1-100 nm) and high specific surface area. The application of nanofertilizers is an up-and-coming field of agricultural research and is an attractive and economical substitute for common fertilizers which can boost global food productivity sustainably. Foliar fertilization is a popular way to satisfy the needs of higher plants. Because of its small application dose, faster nutrient uptake than soil application and relatively less environmental pollution, foliar fertilization is more popular among plants. It can be seen that nanofertilizers and foliar fertilization are the hotspots of attention at present and that current research on the foliar application of nanofertilizers is not as extensive as that on soil application. Based on this background, this paper provides an overview of various applications of foliar spraying of nanofertilizers in agriculture, including applications in improving crop yield and quality as well as mitigating heavy metal stress, salt stress and drought stress.

Enhanced nitrogen photofixation performance of g-C3N4 nanosheets anchored with Bi2O2CO3 and Bi2O3 under simulated solar light

BackgroundPhotocatalytic nitrogen fixation process has been considered an eco-friendly technology. Among visible-light-triggered photocatalysts, g-C3N4 is an excellent choice, due to its some attractive features. Nonetheless, activity limiting factors for photocatalytic proficiency of g-C3N4 are small specific surface area, limited absorption of visible light, fast recombination of photogenerated charges, and poor carrier transportation. MethodsIn this study, we anchored Bi2O2CO3 and Bi2O3 nanoparticles over the nanosheets of g-C3N4 through a facile one-pot refluxing method. The resultant g-C3N4 nanosheet/Bi2O2CO3/Bi2O3 photocatalysts displayed superior photocatalytic nitrogen fixation performance compared to the components. FindingsThe amount of ammonia generation over the optimum nanocomposite was 4064 μmol L−1 g−1, which was 7.89 and 2.19 folds as large as the g-C3N4 and g-C3N4 nanosheet photocatalysts, respectively. The impact of reaction media, Ar atmosphere, solution pH, and electron and hole scavengers was examined on ammonia production to gain more insights into the nitrogen fixation process. Finally, a p-n-n heterojunction mechanism was suggested for the outstanding N2 photofixation reaction over the g-C3N4 nanosheet/Bi2O2CO3/Bi2O3 photocatalysts.

3D/2D photocatalyst fabricated from Pt loading TiO2 nanoparticles and converter slag-derived Fe-doped hydroxyapatite for efficient H2 evolution

H2 generation for partially substituting coke by the photocatalysts fabricated from steel slag presents a desirable approach to on-site carbon footprint reduction in the iron and steel-making industry, both environmentally and economically. However, achieving high photocatalytic H2 production activity is primarily limited by the scarcity of active sites due to a small specific surface area, inefficient charge transfer, and partly restricted by slow kinetics of the H2 generation reaction. In this study, 1 wt% Pt clusters are photo-reduced onto sub-15 nm TiO2 nanoparticles (TiO2-Pt) in 20 vol% methanol. Subsequently, the electrostatic assembling method has been employed to combine steel-making converter slag-derived Fe-doped hydroxyapatite (FeHAp) with TiO2-Pt, forming a type II 3D/2D TiO2-Pt/FeHAp heterojunction. Excellent connectivity between these two phases contributes to efficient charge separation, forming a built-in electric field that drives the photo-generated electrons to flow from FeHAp to the Pt cocatalyst on TiO2 nanoparticles through the type-II path. By the synergistic effects, including the large specific surface of sub-15 nm TiO2, Pt cocatalyst-offered rapid H2 generation kinetics,. and the heterostructure-provided enhancement of interfacial charge migration and separation, 60 mg TiO2-Pt/5FeHAp presents an enhanced H2 production activity in 120 mL of 10 vol% triethanolamine (TEOA), enabling the H2 generation rate (3026 μmol·g−1·h−1) to reach 1.85 and 75.78 times greater than that of pristine TiO2-Pt (1638 μmol·g−1·h−1) and FeHAp-Pt (40 μmol·g−1·h−1), respectively, under UV–visible light irradiation for 3 h at 8 °C and obtaining an apparent quantum yield of 4.72 % at 370 nm. This study provides a promising strategy for green hydrogen-based steel-making in the sustainable development of the steel industry.

Improving the photodegradation efficiency of POPs in oily sewage: Design and synthesis of G-C3N4-based photocatalysts incorporating a pickering emulsion catalytic strategy

Graphitic carbon nitride (g-C3N4) has been intriguing researchers for the preeminent role in water treatment and organic pollutant degradation applications. However, bulk g-C3N4 has bottlenecks such as small specific surface area and insufficient light absorption, reducing the photocatalytic degradation activity. Herein, g-C3N4 photocatalytic nanosheets with high specific surface area were prepared by a morphology control strategy, meanwhile amphiphilic groups were introduced through surface modification to endow the photocatalysts with Pickering particle function, so that they can be stably adsorbed at the micron-scale oil-water emulsion interface to enhance the mass transfer efficiency of oil-water biphasic media. The results showed that the degradation rate of n-hexane model oily sewage was as high as 97.2% by this simple Pickering emulsion (PE) photocatalytic system. Simultaneously, the photocatalytic degradation study was also carried out on an oily sewage sample from the oil production plant in Changqing oilfield, and the degradation rate of the actual oily sewage was 72.3%, which was much higher than that of the bulk-C3N4 photocatalyst (42.9%). This study integrates the photocatalytic technology and PE catalysis and applies them to the treatment of oily sewage, which is an innovative application of emulsion interface photocatalysis and opens up a new perspective for enhancing the photocatalytic activity of g-C3N4.

A study of different grinding aids for low-energy cement clinker production

Cement production requires significant energy, and entails high costs and CO2 emissions. This is because the clinker requires very fine grinding. Grinding aids can improve production and fineness and decrease energy consumption by reducing the agglomeration of particles and protecting the balls and liners in the mill. In this study we compare the effects of three different grinding aids on clinker grinding using a ball mill. A commercial grinding additive, triethanolamine (TEA), and two industrial grinding aids (GAA079 and GAA088) were compared by ball milling tests, with additions of 0.05, 0.25, 0.50 and 1.00 wt%. The industrial grinding aids were characterized using gas chromatography-mass spectrometry (GC-MS). Particle size and morphological analyses were performed using SEM and XRD. The best results were obtained with 0.25% GAA088, which has a higher active component of diethanolamine isopropanolamine (DEIPA) than TEA. The unique combination of TEA and DEIPA in GAA088 enhances grinding efficiency and significantly improves the particle size distribution compared to TEA alone.. The grinding aids produced smooth rounded particles, which have a smaller specific surface area, enhancing the quality of the cement. XRD showed no significant structural distortion with or without grinding aids, and it was also found that the grinding aids helped decrease ball coating during grinding. The use of grinding aids can significantly improve clinker production and fineness while decreasing energy consumption, which can help reduce the costs and CO2 emissions associated with cement production.

Ultrastable quantum dot composites with dense barrier layer for wide color gamut display

Quantum dots (QDs) have showed great potential for next-generation lighting and display technologies. However, its stability is still one of the key problems that limit its practical application. In this paper, by comparing the specific surface area (SSA) and pore width of aluminum oxide (AlOx) and silicon oxide (SiO2) barrier layers, the relationship between the porosity of barrier layers and the stability of QDs was studied. The results showed that the synthesized SiO2-QD-AlOx, which has the smallest SSA in the synthesized QD composites, exhibited the best stability on the quantum dot diffuser plate (QD-DP). Moreover, the operational lifetime (T80) at 450 nm blue light excitation was increased by a factor of 3.41 compared to that of bare QDs. Meanwhile, the prepared QD-DP containing dense SiO2-QD-AlOx composites significantly improved the resistance to light, heat, moisture and oxygen. Finally, the prepared QD-DP was assembled into a Mini-LED TV with a wide color gamut and excellent display performance (a color gamut of 157.4 % for commercial normal TV, and 107.19 % for the National Television System Committee (NTSC 1931)). This technique provides favorable guide for effectively enhancing the stability of QDs in lighting and display technologies.

Nanopore Structure and Multifractal Characteristics of Continental Shale Oil Reservoir: A Case Study from Ziliujing Shales in the Sichuan Basin

Thermal maturity of the shales from the Ziliujing Formation of the Jurassic age in the Sichuan Basin is in the hydrocarbon generation window, which makes it a candidate for shale oil and gas development. The meso- and macropore characteristics and heterogeneity of shales are important factors affecting the occurrence and development of oil and gas. However, the meso- and macropores of the Ziliujing shales have not been systematically studied. Thus, the mineral compositions and total organic carbon (TOC) of samples from this formation, as well as its pore structure, are analyzed by low-temperature N2 adsorption technique. Moreover, the heterogeneity of the pores was determined by multifractal analysis. The results show that the Ziliujing shales can be classified into three types according to the distributions of mineral compositions of carbonate and mixed and argillaceous shales. Results revealed that the smallest meso- and macropore volume (PV), the smallest specific surface area (SSA), and the largest average pore diameter (APD) occur in the carbonate shales. However, the largest PV and SSA and the smallest APD are observed in the argillaceous shales. The porosity of carbonate shales is mainly concentrated between 5 nm and 30 nm. Compared with carbonate shales, the porosity with pore sizes less than 30 nm of mixed and argillaceous shales shows a rapid increase. Furthermore, inorganic minerals are the main factors affecting the pore distributions, while TOC shows a weak effect. Herein, clay minerals significantly increase the mesopore volume and the pore number with a size of less than 30 nm. The Dq-q curves reveal that the meso- and macropore distributions of Ziliujing shales show multifractal behavior, but the multifractal characteristics of pores of various shales are distinctly different. The information dimension D1, the Hurst exponent H, and the width of the right side D0–D10 are key indicators to distinguish the local variations within the pore structure of different types of shales. The carbonate shales have the largest multifractal spectra width and the smallest D1 and H, while the opposite trend is found for the argillaceous shales. Clay minerals reduce the heterogeneity of the meso- and macropore distributions and increase the pore connectivity. Nevertheless, the carbonate minerals exhibit a reverse trend. Finally, it was found that TOC does not impact pore complexity as much. Collectively, this study supports our understanding of the occurrence of shale oil within various reservoir facies, thereby providing a guideline for future explorations in the Ziliujing Formation of the Jurassic age in the Sichuan Basin.

Facile synthesis of g-C3N4 nanosheets for effective degradation of organic pollutants via ball milling

Abstract Graphitic carbon nitride (g-C3N4) has attracted extensive research interest in pollutants remediation. However, the photocatalytic activity of g-C3N4 was significantly limited by its small specific surface area. In this work, a green, high-energy ball milling method was used to fabricate g-C3N4 nanosheets. The structure, morphology, and optical properties of the prepared g-C3N4 nanosheets were characterized. The effect of ball milling parameters on the photocatalytic performance evaluated by Rhodamine B (RhB) and tetracycline (TC) was investigated systemically. Among the tested samples, the g-C3N4 sample milled with a 4 mL isopropanol solution at a rotation speed of 420 rpm, ball-to-powder weight ratio of 10:1, and milling time of 24 h exhibited the highest RhB degradation efficiency of 91.4% and TC degradation efficiency of 70.2%. The enhanced photocatalytic activity after ball milling was ascribed to the increase in specific surface area and efficient separation of electron–hole pairs. The trapping experiment indicated that holes and superoxide radicals were the main active species in the degradation reaction. Moreover, the photocatalytic degradation mechanism of organic pollutants on g-C3N4 nanosheets was also discussed in detail.

Halogenated polymers as a problematic component in the pyrolysis of waste plastics

The study deals with the complications associated with the pyrolysis of a polymer releasing highly corrosive compounds and other products that are difficult to be utilized in practice. Poly(vinyl chloride-vinyl acetate) was chosen as a sample material. This copolymer was subjected to slow pyrolysis up to a temperature of 650 °C, which was achieved with a temperature ramp of 10 °C min‒1. Thermal decomposition took place in a batch apparatus in nitrogen atmosphere. The evaluation of the experiments included a mass balance using an online recording of gas and condensate formation, which was followed by an analysis of the obtained products. The tests showed very small yields of condensates (pyrolysis tar) in the range of 3.0 – 5.5% compared to gas production reaching 71.1 – 72.1% of the raw material weight. Within the discussion, the problem with the production of non-flammable gas consisting mainly of HCl in the initial stages of pyrolysis was highlighted. Under the given conditions, the release of acid gases, in which HCl was gradually replaced by also non-flammable CO2, continued up to about 400 °C. Only gases collected from this temperature above and having a calorific value of 33.5 MJ m‒3 (20 °C / 101.32 kPa) can be considered energetically usable. Condensates mainly represented by a mixture of aromatic hydrocarbons, acetic acid and chlorobenzene were also evaluated as problematic for possible use. The possibilities of physical activation of solid pyrolysis residues by steam at temperatures of 850 and 900 °C were also tested. All experiments led to obtaining products with very small specific surface areas in the range of 1 – 6 m2 g–1. The process loss during activation reached 25 – 33% of the pyrolysis residue weight, depending on the applied temperature and contact time with steam. These values show that the reaction of the activation medium with the sample took place more or less only on the outer surface of the particles and did not lead to the development of an internal porous structure. The achieved results were compared with the identically processed samples of waste tires, which were evaluated as promising in tests carried out in the past. The contrast be-tween the two materials clearly spoke against the discussed copolymer. The results of the experiments can be interpreted, among other things, as a certain warning against attempts at industrial pyrolysis processing of this type of plastic.

Efficient hydrolysis of cellulose to reducing sugars over peanut shell‐derived carbon‐based solid acid with a large surface area

AbstractA carbon‐based solid acid with a large surface area (CSALA; SBET = 237.9 m2/g) was prepared from peanut shells. Compared with a CSA with a small specific surface area (SBET = 5.6 m2/g), the CSALA enabled greater cellulose hydrolysis. Under optimized conditions, the yield of reducing sugars over 2.5 h at 110°C was 60.5% using the CSALA. When a CSA was used, the yield of reducing sugar only reached 58.6% after 4 h at the same temperature. The results showed that the CSALA had higher activity because of its larger specific surface area and more numerous surface acid centers. However, it was unstable and was deactivated after one use. The loss of some of the sulfonic groups on the CSALA surface, and the conversion of some of those groups to sulfate groups under the action of 1‐butyl‐3‐methylimidazolium chloride ionic liquid were the main reasons for the deactivation of the CSALA. In addition, most of the residual sulfonic groups were located in the micropores of CSALA and could not participate in the cellulose hydrolysis reaction.

Conformal BN coating to enhance the electrical insulation and thermal conductivity of spherical graphite fillers for electronic encapsulation field

Herein, we provided a structural design strategy of constructing boron nitride (BN) conformal coating on the surface of the spherical graphite (SG) particles via precursors deposition and high-temperature pyrolysis method to achieve improved electrical insulation. The dissolved and reprecipitated BN precursors were uniformly deposited on the surface of polydopamine-modified SG through strong adhesion and hydrogen bonding of polydopamine. Then, the homogeneous and dense BN ceramic coating was formed on the surface of SG via slow pyrolysis at high temperature. The complete encapsulation of BN coating prevents the SG particles directly contacting with each other in the silicon rubber (SR) matrix to retain electrical insulation of SR composites. Furthermore, the BN coating flattens the uneven surface of SG so that the fillers are better infiltrated by the SR matrix. The small specific surface area of SG@BN filler particles is beneficial to significantly reduce the generation of the filler/matrix interfaces and weaken phonons scattering, thus decreasing the thermal boundary resistance. As a result, the thermal conductivity of prepared SG@BN/SR composites is up to 3.65 W m−1 K−1, which is 20.2-fold of that of pure SR with 0.18 W m−1 K−1. And the SG@BN/SR composites exhibit a satisfactory breakdown voltage of 5.6 kV mm−1, which is much higher than 1.1 kV mm−1 for the original SG/SR composites. This strategy is worth using for reference to extend the application of graphite-type fillers in the electronic encapsulation field.