Showing papers by "Xiaofei Tan published in 2020"

Nitrogen-doped biochar fiber with graphitization from Boehmeria nivea for promoted peroxymonosulfate activation and non-radical degradation pathways with enhancing electron transfer

Abstract: Advanced oxidation has great promise in the degradation of organic pollutants, but the high preparation requirements, adjustment difficulty, high cost, potential hazard, and low repeatability of catalysts limit the practical applications of this technology. In this study, a metal-free biochar-based catalyst derived from biomass fiber was prepared assisted by graphitization and nitrogen incorporation (PGBF-N). The heterogeneous catalysis of peroxymonosulfate (PMS) was triggered by PGBF-N with degradation rate 7 times higher than that of pristine biochar. The high catalytic efficiency was attributed to the accelerated electron transfer originated from the high degree of graphitization and nitrogen functionalization of PGBF-N, in which the non-radical pathways containing carbon-bridge and singlet oxygen-mediated oxidation were elucidated as the predominant pathways for tetracycline degradation, instead of the dominant role of radical pathway in pristine biochar. Vacancies and defective edges formed on sp2-hybridized carbon framework as well as the nitrogen doping sites and ketonic group of PGNF-N were considered as possible active sites. The excellent degradation rate in actual water indicated that the PGBF-N/PMS system dominated by non-radical pathway exhibited a high anti-interference ability to surrounding organic or inorganic compounds. This study provides a facile protocol for converting biomass fiber into functional catalyst and enables underlying insight in mediating dominated degradation mechanism of heterogeneous catalysis by biochar fiber.

Biomass-derived porous graphitic carbon materials for energy and environmental applications

Abstract: As we all know, environmental protection and sustainable energy utilization are significant challenges for us. Due to their many excellent characteristics, carbon materials have been playing a very important role in energy and environmental applications. Biomass is the only renewable carbon source and crucial precursor of carbonaceous materials and has the advantages of a unique structure, a wide range of sources, biodegradability, and low cost. Developing high-performance carbonaceous materials from biomass is a significant research subject. Biomass-derived porous graphitic carbon materials (BPGCs) have received extensive attention as novel high-performance sustainable carbon materials owing to its well-developed porous structure, good graphitic structure, and heteroatom doping. Here, this review firstly focuses on the principal synthesis methodologies of BPGCs. Next, three electrochemical energy storage and conversion systems that utilize BPGCs are intensively investigated, including supercapacitors (SCs), lithium-ion batteries (LIBs) and fuel cells (FCs). Then, BPGCs are further reviewed in terms of their application in the field of environmental protection, which is also the first systematic summary of BPGCs in environmental applications. Finally, this review points out the direction that is worthy of further research in the future and the essential issues that have not yet been resolved.

Design and engineering of layered double hydroxide based catalysts for water depollution by advanced oxidation processes: a review

Abstract: Advanced oxidation processes (AOPs) have attracted special attention owing to the high removal efficiency of recalcitrant organic contaminants. Recently, the use of layered double hydroxides (LDHs) or LDH composites as catalysts for AOPs (photocatalysis, Fenton reaction methods, and sulfate radical (SO4˙−)-mediated oxidations) has received increasing attention and has become a new research hotspot. This is due to their layered structure, flexible tunability, electronic properties, and high physicochemical stability. Herein, we provide a comprehensive review on the development and progress in the synthesis of pristine LDH and modified LDH catalysts for AOPs. Special attention has been paid to the design strategies of high-performance LDHs, including (1) rational design of pristine LDHs, such as binary and ternary LDHs, (2) calcination of LDHs at an appropriate temperature, (3) modification of LDHs with a semiconductor or metal as a cocatalyst, (4) changing the compensating anions, and (5) controlling the LDH morphology. Finally, some valuable perspectives on the challenges and future research directions in LDH-based AOPs are discussed.

Adsorption of 17β-estradiol from aqueous solution by raw and direct/pre/post-KOH treated lotus seedpod biochar.

Abstract: Five biochars derived from lotus seedpod (LSP) were applied to examine and compare the adsorption capacity of 17β-estradiol (E2) from aqueous solution. The effect of KOH activation and the order of activation steps on material properties were discussed. The effect of contact time, initial concentration, pH, ionic strength and humic acid on E2 adsorption were investigated in a batch adsorption process. Experimental results demonstrated that the pseudo second-order model fitted the experimental data best and that adsorption equilibrium was reached within 20 hr. The efficiency of E2 removal increased with increasing E2 concentration and decreased with the increase of ionic strength. E2 adsorption on LSP-derived biochar (BCs) was influenced little by humic acid, and slightly affected by the solution pH when its value ranged from 4.0 to 9.0, but considerably affected at pH 10.0. Low environmental temperature is favorable for E2 adsorption. Chemisorption, π–π interactions, monolayer adsorption and electrostatic interaction are the possible adsorption mechanisms. Comparative studies indicated that KOH activation and the order of activation steps had significant impacts on the material. Post-treated biochar exhibited better adsorption capacity for E2 than direct treated, pre-treated, and raw LSP biochar. Pyrolyzed biochar at higher temperature improved E2 removal. The excellent performance of BCs in removing E2 suggested that BCs have potential in E2 treatment and that the biochar directly treated by KOH would be a good choice for the treatment of E2 in aqueous solution, with its advantages of good efficiency and simple technology.

Three-dimensional microspheric g-C3N4 coupled by Broussonetia papyrifera biochar: facile sodium alginate immobilization and excellent photocatalytic Cr(IV) reduction

Abstract: Photocatalysts comprising Broussonetia papyrifera biochar and g-C3N4 loaded on sodium alginate were prepared and characterized in terms of reusability and photocatalytic Cr(VI) reduction performance. The observed photocurrent responses as well as photoluminescence and UV-visible diffuse reflectance spectra showed that the best-performing catalyst featured the benefits of efficient photogenerated charge separation, superior electron conductance/transfer, and excellent light adsorption ability, which resulted in a higher photocatalytic Cr(VI) reduction performance compared to that of pure g-C3N4 powder. The prepared composite was shown to be reusable and well separable from the reaction mixture, thus being a promising material for the practical photocatalytic removal of Cr(VI) from wastewater. The trapping experiment and XPS spectra of catalysts after reactions confirm that the decontamination of Cr(VI) lies in the photocatalytic reduction of this species into low-toxicity Cr(III) by photoinduced electrons generated from g-C3N4, followed by the adsorption of Cr(III) on biochar or alginate with large specific areas.

Simultaneous remediation of methylene blue and Cr(VI) by mesoporous BiVO4 photocatalyst under visible-light illumination

Abstract: Porous photocatalysts with large surface areas are more photoactive than compact solid counterparts, owing to their larger surface areas and porous structure, which enhance the adsorption and confinement of light, thus improving the reaction between pollutants and photocatalysts. This paper reports the mechanisms involved in the enhanced photocatalytic activity of two kinds of porous BiVO4 catalysts, named p-BVO-1 and p-BVO-2, which are fabricated by a template-free and alcohol-hydrothermal method, respectively. Characterization, photoelectrochemical and optical measurements, reactive species detection, UV–vis, and XPS analyses were conducted. The results show that the introduction of oxygen vacancies and prolonging effect of light within the pore structure can enhance the photon response and charge separation and transfer, which help to elevate the photocatalytic performance. The simultaneous photocatalysis test of p-BVO-1 for methylene blue (MB) and Cr(VI) showed that the addition of Cr(VI) enhanced MB adsorption by forming an MB-Cr-MB complex, and MB promoted the photoreduction of Cr(VI) by scavenging h+ and ⋅O2−, which may oxidize Cr(III) to Cr(VI). The results indicate that ⋅O2− and h+ are mainly deployed to degrade MB, while e− reduces Cr(VI) ions, thereby favoring the separation of electron-hole pairs.

Efficient Removal 17-Estradiol by Graphene-Like Magnetic Sawdust Biochar: Preparation Condition and Adsorption Mechanism

Abstract: The occurrence of environmental endocrine disrupting chemicals (EDCs) in aquatic environments has caused extensive concern. Graphene-like magnetic sawdust biochar was synthesized using potassium ferrate (K2FeO4) to make activated sawdust biochar and applied for the removal of 17-estradiol (E2). The characterization showed that the surface morphology of five graphene-like magnetic sawdust biochars prepared with different preparation conditions were quite different. The specific surface area and pore structure increased with the increment of K2FeO4 addition. The results have shown that graphene-like magnetic sawdust biochar (1:1/900 °C) had the best removal on E2. The experimental results indicated that pseudo-first-order kinetic model and the Langmuir model could describe the adsorption process well, in which the equilibrium adsorption capacity (qe,1) of 1:1/900 °C were 59.18 mg·g−1 obtained from pseudo-first-order kinetic model and the maximum adsorption capacity (qmax) of 1:1/900 °C were 133.45 mg·g−1 obtained from Langmuir model at 298K. At the same time, lower temperatures, the presence of humic acid (HA), and the presence of NaCl could be regulated to change the adsorption reaction in order to remove E2. Adsorption capacity was decreased with the increase of solution pH because pH value not only changed the surface charge of graphene-like magnetic sawdust biochar, but also affected the E2 in the water. The possible adsorption mechanism for E2 adsorption on graphene-like magnetic sawdust biochar was multifaceted, involving chemical adsorption and physical absorption, such as H-bonding, π-π interactions, micropore filling effects, and electrostatic interaction. To sum up, graphene-like magnetic sawdust biochar was found to be a promising absorbent for E2 removal from water.

Coupling of kenaf Biochar and Magnetic BiFeO3 onto Cross-linked Chitosan for Enhancing Separation Performance and Cr(VI) Ions Removal Efficiency.

Abstract: Cr(VI) contamination has posed great threat to both the ecosystem and human health for its carcinogenic and mutagenic nature. A highly effective adsorbent for the removal of Cr(VI) was prepared and its adsorption mechanism was thoroughly discussed in this study. In detail, magnetic BiFeO3 and kenaf biochar were loaded on cross-linked chitosan to obtain chitosan-kenaf biochar@BiFeO3 (CKB) for improving adsorption capacity towards Cr(VI). The adsorption process of Cr(VI) onto CKB was evaluated as a function of the pH, the existence of competing ions, the initial concentration of Cr(VI) and contact time. The results show that CKB exhibits the highest adsorption capacity under the optimal pH 2.0. The presence of competing ions such as Ca2+, NO3-, SO42-, and Cl- decreases the adsorption capacity; among them, Ca2+ and NO3- show the greatest hindrance. By studying the effect of initial Cr(VI) concentration on the adsorption capacity, it was found that CKB in the solution was enough to remove Cr(VI) for all treatments (10-200 mg/L). The adsorption experimental data were well fitted with pseudo-first-order model, suggesting that chemisorption is not the dominant rate-limiting step. Freundlich isotherm model can better explain the adsorption process, indicating a non-ideal adsorption towards Cr(VI) on a heterogeneous surface of CKB. A 25-1 Fractional Factorial Design (FFD) showed that pH and initial concentration of Cr(VI) have significant influence on Cr(VI) adsorption in our reaction system. In general, excellent adsorption efficiency of CKB indicates that it may be a good candidate for the remediation of Cr(VI)-contaminating wastewater.

Synthesis of Porous Biochar Containing Graphitic Carbon Derived From Lignin Content of Forestry Biomass and Its Application for the Removal of Diclofenac Sodium From Aqueous Solution.

Abstract: Porous biochar containing graphitic carbon materials have received great attention from various disciplines, especially for environmental pollutant treatment, due to their cost-effective and specific textural properties. This study exhibited a two-step strategy to compose lignin-porous biochar containing graphitic carbon (LPGC) from pitch pine sawdust and investigated its adsorptive removal for diclofenac sodium (DCF) from an aqueous solution. Sulfuric acid (H2SO4) was utilized to obtain lignin content from biomass and potassium ferrate (K2FeO4) and was adopted to fulfill the synchronous carbonization and graphitization of LPGC. Through slow pyrolysis in atmospheric N2 (900°C - 2 h), the structure of the as-prepared sample was successfully modified. Using SEM images, a stripped layer structure was observed on the H2SO4-treated sample for both one-step and two-step activated samples, indicating the pronounced effect of H2SO4 in the layering of materials. K2FeO4 acted as an activator and catalyst to convert biomass into the porous graphitic structure. The BET surface area, XRD and Raman spectra analyses demonstrated that LPGC possessed a micro/mesoporous structure with a relatively large surface area (457.4 m2 g-1) as well as the presence of a graphitic structure. Further adsorption experiments revealed that LPGC exhibited a high DCF adsorption capacity (qmax = 159.7 mg g-1 at 298 K, pH = 6.5). The effects of ambient conditions such as contact time, solution pH, temperature, ionic strength, electrolyte background on the uptake of DCF were investigated by a batch adsorption experiment. Results indicated that the experimental data were best fitted with the pseudo second-order model and Langmuir isotherm model. Furthermore, the adsorption of DCF onto the LPGC process was spontaneous and endothermic. Electrostatic interaction, H-bonding interaction, and π-π interaction are the possible adsorption mechanisms. The porous biochar containing graphitic carbon obtained from the lignin content of pitch pine sawdust may be a potential material for eliminating organic pollutants from water bodies.

Ramie fiber-based biochar, preparation method and application thereof

Abstract: The invention discloses ramie fiber-based biochar, a preparation method and application thereof. The preparation method of the ramie fiber-based biochar comprises the following steps of: taking ramiefilaments as the raw material to prepare ramie filament biochar, mixing the ramie filament biochar mixed with a deep eutectic solvent, conducting ultrasonic dispersion and carrying out hydrothermal reaction, and conducting pyrolysis carbonization on the obtained ramie fiber biochar, thus obtaining the ramie fiber-based biochar. The ramie fiber-based biochar prepared by the invention has the advantages of large specific surface area, high graphitization degree, good electron transfer performance, high catalytic activity and the like, and is a novel biochar material composed of ramie fiber structure, and the preparation method has the advantages of simple process, strong operability and the like, is suitable for large-scale preparation, and is beneficial to wide application. The ramie fiber-based biochar can be used as an activator for activating persulfate to degrade organic pollutants in water, can realize effective degradation of the organic pollutants, has the advantages of simple operation, high treatment efficiency, strong stability and the like, and has high use value and good application prospect.