Nitrogen-doped carbon nanospheres-modified graphitic carbon nitride with outstanding photocatalytic activity

Metals and metal oxides are widely used as photo/electro-catalysts for environmental remediation. However, there are many issues related to these metal-based catalysts for practical applications, such as high cost and detrimental environmental impact due to metal leaching. Carbon-based catalysts have the potential to overcome these limitations. In this study, monodisperse nitrogen-doped carbon nanospheres (NCs) were synthesized and loaded onto graphitic carbon nitride (g-C3N4, GCN) via a facile hydrothermal method for photocatalytic removal of sulfachloropyridazine (SCP). The prepared metal-free GCN-NC exhibited remarkably enhanced efficiency in SCP degradation. The nitrogen content in NC critically influences the physicochemical properties and performances of the resultant hybrids. The optimum nitrogen doping concentration was identified at 6.0 wt%. The SCP removal rates can be improved by a factor of 4.7 and 3.2, under UV and visible lights, by the GCN-NC composite due to the enhanced charge mobility and visible light harvesting. The mechanism of the improved photocatalytic performance and band structure alternation were further investigated by density functional theory (DFT) calculations. The DFT results confirm the high capability of the GCN-NC hybrids to activate the electron–hole pairs by reducing the band gap energy and efficiently separating electron/hole pairs. Superoxide and hydroxyl radicals are subsequently produced, leading to the efficient SCP removal

Eco-Geological Environment Carrying Capacity and Resource and Environmental Characteristics of Lithium Ore Belt in Western Sichuan

This is an essay in the field of earth sciences. The lithium belt in West Sichuanis the richest area of hard rock lithium resources in China, but the ecological and geological environment in the belt is fragile, so the coordinated development of resources, environment and economy has been a difficult problem for the deep development of regional resources. This paper systematically compares the natural resources, mineral resources, geological environment characteristics and the main environmental geological problems in the lithium belt, constructs an ecological and geological environment carrying capacity evaluation index system based on three subsystems: geological environment, ecological environment and social environment, selects and obtains 19 basic evaluation index data information, and carries out a region-wide carrying capacity evaluation. The results show that: the geological environment of the west Sichuan lithium belt is relatively safe and stable, the existing mining activities in the belt do not have a significant impact on the regional ecological environment, and the impact of human production and life is limited in scope. The proportion of the country area with medium and above carrying capacity reaches 79.16%, the ecological and geological environment carrying capacity in the lithium resource concentration area is high, and the overall ecological and geological environment is in good condition

EFFECT OF TEMPO OXIDATION SYSTEM ON KINETIC CONSTANTS OF COTTON FIBERS

The kinetics of the TEMPO-mediated oxidation of cotton fibers were studied. It was revealed that the oxidation reaction of the cotton fibers by TEMPO/NaBr/NaClO system can be approximately described as two pseudo-first-order reaction kinetics that are based on the cellulose microstructure, namely the kinetic processes of the primary wall and the secondary wall. In the concentration range used in this study, the rate constant k was directly proportional to the concentration of TEMPO. As to NaBr, the rate constant was proportional to the concentration in a relatively lower range, while it tended to level off at higher concentration, but the oxidation reaction rate increased with concentration when the concentration was above 1.0 mmol/g. The pH value had a great impact on the oxidation rate; the optimum pH was controlled from 10 to 11. The effect of temperature on the rate constant could be well described by the Arrhenius equation, and the apparent activation energy measured was about 56.66kJ/mol. The X-ray diffraction pattern, which indicates the crystallinity of cotton fibers, was nearly constant during the oxidation

SURFACE SIZING APPLICATION OF WATERBORNE EPOXY RESIN ON LOW BASIS WEIGHT PAPER

Reducing basis weight could lead to huge savings of forest resources as well as energy consumption and waste treatment in the papermaking process. However, low basis weight paper generally lacks normal strength and stiffness. The lower the basis weight of the paper, the more important is surface sizing. Highly cross-linked cured epoxy resin, due to its epoxy group and phenyl group, has gained such outstanding mechanical properties and dimensional stability that it could be utilized to enhance paper strength and stiffness through surface sizing when incorporated with oxidized starch. In this study, the impacts of sizing volume, fluid temperature, curing agent, and curing system dosage on sizing were investigated. Our results indicated that a rigid resin layer and interpenetrating polymer network formed on the surface and in the inner layer of the paper, respectively. The formed resin layers strongly support the paper and thus resulted in the improvement of strength and stiffness

Molecular Weight Distribution and Dissolution Behavior of Lignin in Alkaline Solutions

Lignin, as the sole renewable aromatic resource in nature, has great potential for replacing fossil resources. However, the complexity of its structure limits its high value utilization, and the molecular weight distribution and dissolution behavior of lignin in alkaline solutions is still unclear. In this study, a conventional lignin separation during the pulping process in an alkaline hydrothermal system was performed by controlling the amount of NaOH, reaction temperature and holding time. Various analysis methods, including GPC, 2D–HSQC NMR and FTIR were used to study the characteristics of lignin fragments dissolved from wood. We were aiming to understand the rule of lignin dissolution and the recondensation mechanism during the process. The results showed dissolution of lignin due to ether bond fracturing by OH− attacking the Cα or Cβ positions of the side chain with penetration of NaOH, and the lignin fragments in solution recondensed into complex lignin with more stable C–C bonds. The experimental results also prove that the average molecular weight increased from 4337 g/mol to 11,036 g/mol and that holding time from 60 min to 120 min at 150 °C with 14 wt% of NaOH

Biosorption of Heavy Metal Ions from Aqueous Solution on Chinese Fir Bark Modified by Sodium Hypochlorite

The oxidation conditions and adsorption ability of Cu (II), Cd (II), and Pb (II) from an aqueous solution of sodium hypochlorite-oxidized fir bark powder were investigated. The optimum amount of NaClO was 9.6%, the pH was 9, and the oxidation time was 120 min. Batch adsorption experiments were carried out with various times, pH values, and initial metal ion concentrations. The adsorption isotherms and kinetics of adsorption were also studied. The maximum adsorption capacity of oxidized fir bark was 0.983, 1.223, and 0.966 mmol/g for Cu (II), Cd (II), and Pb (II), respectively, within 30 min at pH 5, higher adsorption capacity than that of unoxidized fir bark. The isothermal adsorption of heavy metal ions in aqueous solution was a good fit to the Langmuir equation, with a coefficient of determination, R2, above 0.99. The adsorption of fir bark on metal ions can be appropriately approximated by a pseudo-second order adsorption kinetics model. Results indicate that the fir bark powder modified with sodium hypochlorite can adsorb large amounts of metal ions and could be a good adsorbent for the removal of Cu(II), Cd(II), and Pb(II) from aqueous solution

Starch-Based Flexible Coating for Food Packaging Paper with Exceptional Hydrophobicity and Antimicrobial Activity

Herein, we fabricated a starch-based flexible coating for food packaging papers with excellent hydrophobicity and antimicrobial properties. FTIR (Fourier transform infrared) and XRD (X-ray diffraction) spectra revealed the homogeneous dispersion of the ZnO nanoparticles (NPs) in the composite film within 5% ZnO NP dosage. SEM (scanning electron microscope) and AFM (atomic force microscope) micrographs confirmed the increased roughness on the composite film with the increased dosages of ZnO NPs. Hydrophobic characteristics showed that dramatic enhancement was obtained in the values and stabilities of DCAs (dynamic contact angles) in the resultant film and coated paper. TG (thermogravimetry) results demonstrated the increased thermal stabilities of the composite films. Significantly, a decreased water vapor transmission rate was observed in the coated paper. When 20% guanidine-based starch and 2% CMC (carboxy methyl cellulose) was added, a flexible coating with excellent antimicrobial activity towards Escherichia coli can be obtained. Furthermore, the migration of ZnO NPs into the food simulants was well below the overall migration legislative limit. The resultant starch-based flexible composite film and coated paper established an effective approach to develop a green-based material for food packaging applications

Silver Nanoparticle-Embedded Conductive Hydrogels for Electrochemical Sensing of Hydroquinone

In this work, a conductive hydrogel was successfully synthesized, taking advantage of the high number density of active amino and hydroxyl groups in carboxymethyl chitosan and sodium carboxymethyl cellulose. These biopolymers were effectively coupled via hydrogen bonding with the nitrogen atoms of the heterocyclic rings of conductive polypyrrole. The inclusion of another biobased polymer, sodium lignosulfonate (LS), was effective to achieve highly efficient adsorption and in-situ reduction of silver ions, leading to silver nanoparticles that were embedded in the hydrogel network and used to further improve the electro-catalytic efficiency of the system. Doping of the system in the pre-gelled state led to hydrogels that could be easily attached to the electrodes. The as-prepared silver nanoparticle-embedded conductive hydrogel electrode exhibited excellent electro-catalytic activity towards hydroquinone (HQ) present in a buffer solution. At the optimum conditions, the oxidation current density peak of HQ was linear over the 0.1–100 μM concentration range, with a detection limit as low as 0.12 μM (signal-to-noise of 3). The relative standard deviation of the anodic peak current intensity was 1.37% for eight different electrodes. After one week of storage in a 0.1 M Tris-HCl buffer solution at 4 °C, the anodic peak current intensity was 93.4% of the initial current intensity. In addition, this sensor showed no interference activity, while the addition of 30 μM CC, RS, or 1 mM of different inorganic ions does not have a significant impact on the test results, enabling HQ quantification in actual water samples.Applied Science, Faculty ofChemical and Biological Engineering, Department ofReviewedFacultyResearche

Characterization of Polypropylene Fiber and Lignocresol Enhanced Poly(3-hydroxybutyrate) Composite Films

The depletion of fossil resources and the environmental impact of petroleum-based plastic materials have driven a strong global interest in renewable biobased polymers and composites derived from natural resources. Since biodegradable polymers have their own drawbacks, it is often combined as a composite with other fillers. Polypropylene (PP)/Poly(3-hydroxybutyrate) (PHB) composite films and lignocresol (LC)/PP/PHB composite films were cast by blending methods. This study investigated the effects of the amounts of added PP fiber and LC on the mechanical and thermal properties in the corresponding composite films. The overall properties of LC/PP/PHB composite films were best with 8 wt.% PP fiber content and 3 wt.% LC content. The tensile strength (13.00 MPa) was up to 1.25 times that of the original PHB film (10.44 MPa), and the thermal properties of the composite films were improved by adding 3 wt.% LC. Thermogravimetry (TG) analysis indicated that the onset temperature (382.0 °C) rose by 50.7 °C compared with PP/PHB film (331.3 °C), and the residual mass was close to 0%

Manufacture of Highly Transparent and Hazy Cellulose Nanofibril Films via Coating TEMPO-Oxidized Wood Fibers

Traditionally, inorganic nanoparticles (SiO2, TiO2) have been utilized to tune the optical haze of optoelectronic devices. However, restricted to complex and costly processes for incorporating these nanoparticles, a simple and low-cost approach becomes particularly important. In this work, a simple, effective, and low-cost method was proposed to improve optical haze of transparent cellulose nanofibril films by directly depositing micro-sized 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized wood fibers (“coating” method). The obtained films had a high total transmittance of 85% and a high haze of 62%. The film samples also showed a high tensile strength of 80 MPa and excellent thermal stability. Dual sides of the obtained films had different microstructures: one side was extremely smooth (root-mean-square roughness of 6.25 nm), and the other was extremely rough (root-mean-square roughness of 918 nm). As a reference, micro-sized TEMPO-oxidized wood fibers and cellulose nanofibrils were mixed to form a transparent and hazy film (“blending” method). These results show that hazy transparent films prepared using the “coating” method exhibit superior application performances than films prepared using the “blending” method