Transformation, Morphology, and Dissolution of Silicon and Carbon in Rice Straw-Derived Biochars under Different Pyrolytic Temperatures

Biochars are increasingly recognized as environmentally friendly and cheap remediation agents for soil pollution. The roles of silicon in biochars and interactions between silicon and carbon have been neglected in the literature to date, while the transformation, morphology, and dissolution of silicon in Si-rich biochars remain largely unaddressed. In this study, Si-rich biochars derived from rice straw were prepared under 150–700 °C (named RS150-RS700). The transformation and morphology of carbon and silicon in biochar particles were monitored by FTIR, XRD, and SEM-EDX. With increasing pyrolytic temperature, silicon accumulated, and its speciation changed from amorphous to crystalline matter, while the organic matter evolved from aliphatic to aromatic. For rice straw biomass containing amorphous carbon and amorphous silicon, dehydration (<250 °C) made silicic acid polymerize, resulting in a closer integration of carbon and silicon. At medium pyrolysis temperatures (250–350 °C), an intense cracking of carbon components occurred, and, thus, the silicon located in the inside tissue was exposed. At high pyrolysis temperatures (500–700 °C), the biochar became condensed due to the aromatization of carbon and crystallization of silicon. Correspondingly, the carbon release in water significantly decreased, while the silicon release somewhat decreased and then sharply increased with pyrolytic temperature. Along with SEM-EDX images of biochars before and after water washing, we proposed a structural relationship between carbon and silicon in biochars to explain the mutual protection between carbon and silicon under different pyrolysis temperatures, which contribute to the broader understanding of biochar chemistry and structure. The silicon dissolution kinetics suggests that high Si biochars could serve as a novel slow release source of biologically available Si in low Si agricultural soils

Down-Cycling Sustainability of Flexible Polyurethane Foam in Improving Asphalt Performance through a Proper Pyrolysis Approach

The down-cycling process of waste polymers in asphalt binder achieves a win–win situation in terms of economic modification and efficient disposal of valuable waste. By combining the “controllable pyrolysis” and “down-cycling” concepts, this study specified the application potential of sustainable recycling flexible polyurethane foam (FPUF) in improving asphalt performance. A proper pyrolysis method was proposed to selectively decompose waste FPUF into fibers. Subsequently, eco-friendly and cost-effective properly pyrolyzed FPUF fiber-modified asphalt (PyFMA) was developed. The microscopic, chemical, and mechanical investigations were carried out to clarify modification mechanisms and application feasibility. The results showed that the proper pyrolysis method efficiently produced flexible reticulated PFUF fibers of different sizes grafted with polar groups. The PFUF fibers interlocked spatially and well-coordinated with the asphalt matrix, contributed an elastic component in the mixed hybrid, and positively influenced the asphalt performance. The performance enhancement was the result of a combination of chemical interaction, physical reinforcement, and the volumetric filling effect. In addition, the PyFMA had adequate workability at a high fiber dosage of 24% to achieve a massive recycling goal. It is promising and feasible to use waste FPUF as a sustainable and high-performance asphalt modifier, which countermeasures the rapidly increasing abandonment and meets economical asphalt modification requirements

Quantification of Chemical States, Dissociation Constants and Contents of Oxygen-containing Groups on the Surface of Biochars Produced at Different Temperatures

Surface functional groups such as carboxyl play a vital role in the environmental applications of biochar as a soil amendment. However, the quantification of oxygen-containing groups on a biochar surface still lacks systematical investigation. In this paper, we report an integrated method combining chemical and spectroscopic techniques that were established to quantitatively identify the chemical states, dissociation constants (p<i>K</i>_a), and contents of oxygen-containing groups on dairy manure-derived biochars prepared at 100–700 °C. Unexpectedly, the dissociation pH of carboxyl groups on the biochar surface covered a wide range of pH values (pH 2–11), due to the varied structural microenvironments and chemical states. For low temperature biochars (≤350 °C), carboxyl existed not only as hydrogen-bonded carboxyl and unbonded carboxyl groups but also formed esters at the surface of biochars. The esters consumed OH^– via saponification in the alkaline pH region and enhanced the dissolution of organic matter from biochars. For high temperature biochars (≥500 °C), esters came from carboxyl were almost eliminated via carbonization (ester pyrolysis), while lactones were developed. The surface density of carboxyl groups on biochars decreased sharply with the increase of the biochar-producing temperature, but the total contents of the surface carboxyls for different biochars were comparable (with a difference <3-fold) as a result of the expanded surface area at high pyrolytic temperatures. Understanding the wide p<i>K</i>_a ranges and the abundant contents of carboxyl groups on biochars is a prerequisite to recognition of the multifunctional applications and biogeochemical cycling of biochars

IrMo Nanocluster-Doped Porous Carbon Electrocatalysts Derived from Cucurbit[6]uril Boost Efficient Alkaline Hydrogen Evolution

Electrocatalysts based on noble metals have been proven efficient for high-purity hydrogen production. However, the sluggish kinetics of the hydrogen evolution reaction (HER) in alkaline media caused by high water dissociation energy largely hampers this electrochemical process. To improve the electrocatalytic activity, we fabricate an effective porous carbon matrix derived from cucurbit[6]uril using a template-free method to support iridium–molybdenum (IrMo) nanoclusters. As proof of concept, the resulting IrMo-doped carbon electrocatalyst (IrMo-CBC) was found to boost the alkaline HER significantly. Owing to the unique in-plane hole structure and the nitrogen-rich backbone of cucurbit[6]uril as well as the ultrafine IrMo nanoclusters, IrMo-CBC exhibits pronounced alkaline HER activity with an extremely low overpotential of 12 mV at 10 mA cm–2, an ultrasmall Tafel slope (28.06 mV dec–1), a superior faradic efficiency (98%), and a TOF of 11.6 H2 s–1 at an overpotential of 50 mV, outperforming most iridium-based electrocatalysts and commercial Pt/C

Photoelectrochemical Water Splitting SystemA Study of Interfacial Charge Transfer with Scanning Electrochemical Microscopy

Fast charge transfer kinetics at the photoelectrode/electrolyte interface is critical for efficient photoelectrochemical (PEC) water splitting system. Thus, far, a measurement of kinetics constants for such processes is limited. In this study, scanning electrochemical microscopy (SECM) is employed to investigate the charge transfer kinetics at the photoelectrode/electrolyte interface in the feedback mode in order to simulate the oxygen evolution process in PEC system. The popular photocatalysts BiVO₄ and Mo doped BiVO₄ (labeled as Mo:BiVO₄) are selected as photoanodes and the common redox couple [Fe­(CN)₆]^3–/[Fe­(CN)₆]^4– as molecular probe. SECM characterization can directly reveal the surface catalytic reaction kinetics constant of 9.30 × 10⁷ mol^–1 cm³ s^–1 for the BiVO₄. Furthermore, we find that after excitation, the ratio of rate constant for photogenerated hole to electron via Mo:BiVO₄ reacting with mediator at the electrode/electrolyte interface is about 30 times larger than that of BiVO₄. This suggests that introduction of Mo⁶⁺ ion into BiVO₄ can possibly facilitate solar to oxygen evolution (hole involved process) and suppress the interfacial back reaction (electron involved process) at photoanode/electrolyte interface. Therefore, the SECM measurement allows us to make a comprehensive analysis of interfacial charge transfer kinetics in PEC system

Sugar Cane-Converted Graphene-like Material for the Superhigh Adsorption of Organic Pollutants from Water via Coassembly Mechanisms

A sugar cane-converted graphene-like material (FZS900) was fabricated by carbonization and activation. The material exhibited abundant micropores, water-stable turbostratic single-layer graphene nanosheets, and a high BET-N₂ surface area (2280 m² g^–1). The adsorption capacities of FZS900 toward naphthalene, phenanthrene, and 1-naphthol were 615.8, 431.2, and 2040 mg g^–1, respectively, which are much higher than those of previously reported materials. The nonpolar aromatic molecules induced the turbostratic graphene nanosheets to agglomerate in an orderly manner, forming 2–11 graphene layer nanoloops, while polar aromatic compounds induced high dispersion or aggregation of the graphene nanosheets. This phase conversion of the nanosized materials after sorption occurred through coassembly of the aromatic molecules and the single-layer graphene nanosheets via large-area π–π interactions. An adsorption-induced partition mechanism was further proposed to explain the nanosize effect and nanoscale sorption sites observed. This study indicates that commonly available biomass can be converted to graphene-like material with superhigh sorption ability in order to remove pollutants from the environment via nanosize effects and a coassembly mechanism

Production Scheduling of a Large-Scale Steelmaking Continuous Casting Process via Unit-Specific Event-Based Continuous-Time Models: Short-Term and Medium-Term Scheduling

The scheduling of steelmaking continuous-casting (SCC) processes is of major importance in iron and steel operations, since it is often a bottleneck in iron and steel production. Optimal scheduling of SCC processes can increase profit, minimize production cost, reduce material and energy consumption, and improve customer satisfaction. Scheduling of SCC processes is challenging, because of its combinatorial nature, complex practical constraints, and strict requirements on material continuity and flow time, as well as the technological requirements to ensure practical feasibility of the resulting scheduling. In this paper, we first develop a novel unit-specific event-based continuous-time mixed-integer linear optimization (MILP) model for this problem and incorporate several realistic operational features. Then, we extend the rolling horizon approach proposed by Lin et al. [Lin et al. <i>Ind. Eng. Chem. Res.</i> <b>2002</b>, <i>41</i>, 3884–3906] and Janak et al. [Janak et al. <i>Ind. Eng. Chem. Res.</i> <b>2006</b>, <i>45</i>, 8234–8252] to solve this large-scale and complex optimization problem. Four large-scale industrial problems are used to illustrate the efficiency and effectiveness of the proposed formulation and rolling horizon approach. The computational results show that the extended rolling horizon approach successfully solves the large-scale case studies and results in the same or better integer solution than that obtained from directly solving the entire scheduling model

Sorption of Poly- and Perfluoroalkyl Substances (PFASs) Relevant to Aqueous Film-Forming Foam (AFFF)-Impacted Groundwater by Biochars and Activated Carbon

Despite growing concerns about human exposure to perfluorooctanoate (PFOA) and perfluorooctanesulfonate (PFOS), other poly- and perfluoroalkyl substances (PFASs) derived from aqueous film-forming foams (AFFFs) have garnered little attention. While these other PFASs may also be present in AFFF-impacted drinking water, their removal by conventional drinking-water treatment is poorly understood. This study compared the removal of 30 PFASs, including 13 recently discovered PFASs, from an AFFF-impacted drinking water using carbonaceous sorbents (i.e., granular activated carbon, GAC). The approach combined laboratory batch experiments and modeling: batch sorption data were used to determine partition coefficients (<i>K</i>_d) and calibrate a transport model based on intraparticle diffusion-limited sorption kinetics, which was used to make forward predictions of PFAS breakthrough during GAC adsorption. While strong retention was predicted for PFOS and PFOA, nearly all of the recently discovered polyfluorinated chemicals and PFOS-like PFASs detected in the AFFF-impacted drinking water were predicted to break through GAC systems before both PFOS and PFOA. These model breakthrough results were used to evaluate a simplified approach to predicting PFAS removal by GAC using compound-specific retention times on a C18 column (RT_C18). Overall, this study reveals that GAC systems for the treatment of AFFF-impacted sources of water for PFOA and PFOS likely achieve poor removal, when operated only for the treatment of PFOS and PFOA, of many unmonitored PFASs of unknown toxicity

Generating Huge Magnetocurrent by Using Spin-Dependent Dehydrogenation Based on Electrochemical System

Systems featuring large magnetocurrent (MC) at room temperature are attractive owing to their potential for application in magnetic field sensing. Usually, the magnetic materials are exploited to achieve large MC effect. Here, we report a huge MC of up to 150% in a nonmagnetic system based on the electrochemical oxidation of hydrazine at room temperature. The huge MC is ascribed to the spin-dependent N–H bond cleavage and reformation through dehydrogenation during the oxidation of hydrazine. Specifically, the N–H bond cleavage generates singlet radical pairs. An external magnetic field can accelerate the spin evolution from singlet to triplet in spin-correlated radical pairs by perturbing spin precessions. Increasing the amount of triplet radical pairs can largely reduce the N–H bond recovery and significantly enhance the oxidation current of hydrazine. As a consequence, the spin-dependent bond formation through dehydrogenation can provide a new approach to generate huge MC in electrochemical cells