Conversion of Lignin into Porous Carbons for High-Performance Supercapacitors via Spray Drying and KOH Activation: Structure-Properties Relationship and Reaction Mechanism

Lignin-derived porous carbons have emerged as promising electrode materials for supercapacitors.However,the challenge remains in designing and controlling their structure to achieve ideal electrochemical performance due to the complex molecular structure of lignin and its intricate chemical reactions during the activation process.In this study,three porous carbons were synthesized from lignin by spray drying and chemical activation with vary-ing KOH ratios.The specific surface area and structural order of the prepared porous carbon continued to increase with the increase of the KOH ratio.Thermogravimetric-mass spectrometry(TG-MS)was employed to track the molecular fragments generated during the pyrolysis of KOH-activated lignin,and the mechanism of the thermochemical conversion was investigated.During the thermochemical conversion of lignin,KOH facili-tated the removal of H2 and CO,leading to the formation of not only more micropores and mesopores,but also more ordered carbon structures.The pore structure exhibited a greater impact than the carbon structure on the electrochemical performance of porous carbon.The optimized porous carbon exhibited a capacitance of 256 F g-1 at a current density of 0.2 A g-1,making it an ideal electrode material for high-performance supercapacitors.

CoN_(x)C active sites-rich three-dimensional porous carbon nanofibers network derived from bacterial cellulose and bimetal-ZIFs as efficient multifunctional electrocatalyst for rechargeable Zn–air batteries

In this work, a CoNxC active sites-rich three-dimensional porous carbon nanofibers network derived from bacterial cellulose and bimetal-ZIFs is prepared via a nucleation growth strategy and a pyrolysis process.The material displays excellent electrocatalytic activity for the oxygen reduction reaction, reaching a high limiting diffusion current density of -7.8 mA cm^(-2), outperforming metal–organic frameworks derived multifunctional electrocatalysts, and oxygen evolution reaction and hydrogen evolution reaction with low overpotentials of 380 and 107 mV, respectively. When the electrochemical properties are further evaluated, the electrocatalyst as an air cathode for Zn-air batteries exhibits a high cycling stability for63 h as well as a maximum power density of 308 mW cm^(-2), which is better than those for most Zn-air batteries reported to date. In addition, a power density of 152 mW cm^(-2) is provided by the solid-state Zn-air batteries, and the cycling stability is outstanding for 24 h. The remarkable electrocatalytic properties are attributed to the synergistic effect of the 3 D porous carbon nanofibers network and abundant inserted CoNxC active sites, which enable the fast transmission of ions and mass and simultaneously provide a large contact area for the electrode/electrolyte.

Electro-enhanced adsorption of As(V)by activated carbon in three-dimensional electrode reactor

This study focused on As(V)removal by electrosorption in a self-made three-dimensional electrode reactor,in which granular activated carbon(GAC)was used as the particle electrode.Under the optimal conditions,the removal efficiency of As(V)was 84%,and its residual concentration in solution was 0.08 mg/L.From kinetic investigation,the rate determining steps of the entire process may involve more than two processes:membrane diffusion,material diffusion and physical/chemical adsorption processes.During the desorption process,As(V)can be desorbed from GAC,and the GAC was able to electro-adsorb As(V)again after desorption,which means that the electrode has good cycling performance.

Preparation and Electrochemical Performance Study of Catalytic Cracking Oil Slurry-based Porous Carbon Materials

Catalytic cracking oil slurry is a by-product of catalytic cracking projects,and the efficient conversion and sustainable utilization of this material are issues of continuous concern in the petroleum refining industry.In this study,oxygen-enriched activated carbon is prepared using a one-step KOH activation method with catalytic cracking oil slurry as the raw material.The as-prepared oil slurry-based activated carbon exhibits a high specific surface area of 2102 m^(2)/g,welldefined micropores with an average diameter of 2 nm,and a rich oxygen doping content of 32.97%.The electrochemical performance of the nitrogen-doped porous carbon is tested in a three-electrode system using a 6 mol/L KOH solution as the electrolyte.It achieves a specific capacitance of up to 230 F/g at a current density of 1 A/g.Moreover,the capacitance retention rate exceeds 89%after 10000 charge and discharge cycles,demonstrating excellent cycle stability.This method not only improves the utilization efficiency of industrial fuel waste but also reduces the production cost of supercapacitor electrode materials,thereby providing a simple and effective strategy for the resource utilization of catalytic cracking oil slurries.

Effects of Microporous Structure of Activated Carbon on Adsorption Performance of N-butane

[Objective] The paper was to study the effect of microporous structure of ac- tivated carbon on adsorption performance of n-butane. [Method] Using 8 activated car- bons prepared from different materials and technologies, the effects of physical prop- erties of activated carbon on butane adsorption performance were investigated. [Result] Specific surface area, pore volume and pore size distribution of activated carbon exert- ed remarkable effects on butane adsorption. The activated carbon with high percent- age of micropore volume within the range of 1.2-2 nm possessed high butane activity. The level of butane retentivity rose with the increase of the volume of pore within the range of 0.5-0,9 nm, which led to smaller butan working capacity （BWC）. [Conclusion] The study provided reference for the adsorption research for activated carbon.

Controlled-Release of Plant Volatiles:New Composite Materials of Porous Carbon-Citral and Their Fungicidal Activity against Exobasidium vexans

Citral(Eo)exhibits excellent fungicidal activities.However,it is difficult to maintain long-term fungicidal activity due to its strong volatility.Herein,a controlled-release strategy by using biomass-derived porous carbon(BC)was developed to overcome the drawback of Eo.New composite materials were prepared by loading Eo on tea stem porous carbon(BC@Eo),and their controlled-release fungicidal activity against Exobasidium vexans was assessed.BC with a large specific surface area of 1001.6 m2/g and mesoporous structure was fabricated through carbonization tempera-ture of 700℃.The BC@Eo materials were characterized using Fourier-transform infrared spectroscopy and X-ray powder diffraction.The results suggested that chemical and physical interactions occurred in BC@Eo.The Eo release profile suggested a biphasic pattern with an initial fast release on days 1–14 and a subsequent controlled phase on days 14–30.The in vitro cumulative release percentage of Eo from BC@Eo was 51%during one month,and this result was significantly lower than that from free Eo(cumulative release percentage of Eo of 82%in one week).The anti-fungal activities of Eo and BC@Eo against E.vexans were determined using the inhibition zone method.The results indicated that Eo and BC@Eo formed large inhibition zones of 19.66±0.79 and 21.92±0.77 mm,respectively.The influence on the hyphal structure of E.vexans was observed by scanning electron microscopy on day 30.The hyphal structure of E.vexans treated with BC@Eo was more shrunken than that treated with Eo at 30 days,suggesting that BC@Eo prolongs the fungicidal activity against E.vexans.This study demonstrated that the encapsulation of Eo in BC for developing the BC@Eo materials could be a promising strategy to inhibit volatility and maintain the fungicidal activity of Eo and provide a potential alternative for the reuse of abundant tea biomass waste resources.

In-situ formation of cobalt phosphide nanoparticles confined in three-dimensional porous carbon for high-performing zinc-air battery and water splitting

The rational design of efficient and stable carbon-based electrocatalysts for oxygen reduction and oxygen evolution reactions is crucial for improving energy density and long-term stability of rechargeable zinc-air batteries(ZABs).Herein,a general and controllable synthesis method was developed to prepare three-dimensional(3D)porous carbon composites embedded with diverse metal phosphide nanocrystallites by interfacial coordination of transition metal ions with phytic acid-doped polyaniline networks and subsequent pyrolysis.Phytic acid as the dopant of polyaniline provides favorable anchoring sites for metal ions owing to the coordination interaction.Specifically,adjusting the concentration of adsorbed cobalt ions can achieve the phase regulation of transition metal phosphides.Thus,with abundant cobalt phosphide nanoparticles and nitrogen-and phosphorus-doping sites,the obtained carbon-based electrocatalysts exhibited efficient electrocatalytic activities toward oxygen reduction and evolution reactions.Consequently,the fabricated ZABs exhibited a high energy density,high power density of 368 mW cm^(-2),and good cycling/mechanical stability,which could power water splitting for integrated device fabrication with high gas yields.

Optimization of Fixed-Bed Design for Natural Gas Mercury Removal by Sulfur Doped into Porous Activated Carbon

The present work reports the synthesis and application of sulfur doped into porous activated carbon for removing elemental mercury from natural gas using a bench-scale fixed-bed reactor. A series of experiments were carried out to investigate the optimization of Hg0 capture. Furthermore, our experimental results about optimum conditions to remove Hg0 were 1:10 of sulfur to activated carbon impregnation ratio, 350°C of impregnation temperature, and 3 hours of impregnation time. This research showed that the prepared adsorbents were capable to remove remarkable amount of Hg0 (23.615 mg/g) at high adsorption efficiency. This study may serve as reference on natural gas power plants for the removal of Hg0 using the same conditions.

Regeneration of activated carbon adsorbed EDTA by electrochemical method

Activated carbon after saturated adsorption of EDTA was used as particle electrode in a three-dimensional electrode reactor to treat EDTA-containing wastewater.Electrochemical method was used to regenerate activated carbon after many times of electrolysis.Based on the analysis of infrared spectra of activated carbon after adsorption and repeated electrolysis,EDTA was degraded into glycine,and then non-catalytic activated associated complex was formed with N—H bond on the activated carbon.The catalytic ability of the activated carbon vanished and the EDTA degradation efficiency was dropped.Activated carbon could be effectively regenerated by electrochemical method in the three-dimensional reactor.Effects of electric current,conductivity and pH on activated carbon regeneration were investigated,and the optimum conditions were concluded as follows：100-300 mA of current intensity,1.39 mS/cm of electric conductivity,60 min of electrolysis time and pH 6.0-8.0.Under the optimized conditions,the activity of the activated carbon can be recovered and the residual total organic carbon（TOC） was below 10 mg/L（the initial TOC was 200 mg/L） in the three-dimensional electrode reactor.

Biomass Straw Based Activated Porous Carbon Materials for High-Performance Supercapacitors

Biomass straws are often regarding as agricultural waste, usually burned off in rural areas, which results in severe resource waste andair pollution. In this work, biomass-based porous carbon material with a lamellar microstructure is obtained via simple hydrothermaland subsequent KOH activation, the optimum activate process is determined by the proportion of activator. Scanning electronmicroscopy (SEM) and nitrogen adsorption techniques are conducted to investigate the physical properties of the materials. Cyclicvoltammetry and constant current discharge/charge in the three-electrode system and symmetrical double-layer capacitors resultsindicate the best electrochemical performance of SCA-1.5 electrode material, with a capacity of 250.0 F g-1 at 1.0 A g-1. And notably,high recycling stability at a high cycling rate of 1.0 A g-1 after 18,000 cycles.

KOH activated carbon derived from biomass-banana fibers as an efficient negative electrode in high performance asymmetric supercapacitor

Here we demonstrate the fabrication, electrochemical performance and application of an asymmetric supercapacitor (AS) device constructed with ss-Ni(OH)(2)/MWCNTs as positive electrode and KOH activated honeycomb-like porous carbon (K-PC) derived from banana fibers as negative electrode. Initially, the electrochemical performance of hydrothermally synthesized ss-Ni(OH)(2)/MWCNTs nanocomposite and K-PC was studied in a three-electrode system using 1 M KOH. These materials exhibited a specific capacitance (Cs) of 1327 Fig and 324 F/g respectively at a scan rate of 10 mV/s. Further, the AS device i.e., ss-Ni(OH)(2)/MWCNTs// K-PC in 1 M KOH solution, demonstrated a Cs of 156 F/g at scan rate of 10 mV/s in a broad cell voltage of 0-2.2 V. The device demonstrated a good rate capability by maintaining a Cs of 59 F/g even at high current density (25 A/g). The device also offered high energy density of 63 Wh/kg with maximum power density of 5.2 kW/kg. The AS device exhibited excellent cycle life with 100% capacitance retention at 5000th cycle at a high current density of 25 A/g. Two AS devices connected in series were employed for powering a pair of LEDs of different colors and also a mini fan. (C) 2016 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.

STUDY ON THE PROPERTIES OF DIFFERENT ACTIVATED CARBON FIBERS AND THEIR ADSORPTION CHARACTERISTICS FOR FORMALDEHYDE

Porous structure and surface chemistry of activated carbon fibers obtained by differ-ent precursors and activation methods were investigated. Adsorption isotherms werecharacterized by nitrogen adsorption at 77K over a relative pressure range from 10 6to 1. The regularization method according to Density Functional Theory (DFT) wasemployed to calculate the pore size distribution in the samples. Their specific surfaceareas were calculated by BET method, micropore volume and microporous specificsurface area calculated by t-plot method and MPD by Horvath-Kawazoe equation. Mi-cropore volume of rayon-based ACF was higher than that of other samples. The staticand dynamic adsorption capacity for formaldehyde on different ACFs was determined.The results show that steam activated Rayon-based A CFs had higher adsorption capac-ity than that of steam and KOH activated PAN-A CFs. Breakthrough curves illustratedthat Rayon-ACFs had longer breakthrough time, thus they possessed higher adsorp-tion capacity for formaldehyde than that of PAN-ACFs. The entire sample had smalladsorption capacity and short breakthrough time for water. Rayon-A CFs had exccl-lent adsorption selectivity for formaldehyde than PAN-ACFs. And the samples withhigh surface areas had relatively high adsorption capacity for formaldehyde. Elementaicontent of different A CFs were performed. Rayon-based A CFs contained more oxygenthan PAN-ACFs, which may be attributed to their excellent adsorption capacity forformaldehyde.

Fibrous TiO_2 prepared by chemical vapor deposition using activated carbon fibers as template via adsorption,hydrolysis and calcinations

TiO2 fibers were prepared via alternatively introducing water vapor and Ti precursor carried by N2 to an APCVD （chemical vapor deposition under atmospheric pressure） reactor at ≤200 ℃. Activated carbon fibers （ACFs） were used as templates for deposition and later removed by calcinations. The obtained catalysts were characterized by scanning electron micros- copy （SEM）, transmission electron microscopy （TEM）, Brunauer, Emmett and Teller （BET） and X-ray diffraction （XRD） analysis The pores within TiO2 fibers included micro-range and meso-range, e.g., 7 nm, and the specific surface areas for TiO2 fibers were 141 m^2/g and 148 m^2/g for samples deposited at 100 ℃ and 200℃ （using ACFI700 as template）, respectively. The deposition temperature significantly influenced TiO2 morphology. The special advantages of this technique for preparing porous nano-material include no consumption of organic solvent in the process and easy control of deposition conditions and speeds.

Porous Carbon from Corn Flour Prepared by H₃PO₄Carbonization Combined with KOH Activation for Supercapacitors

Hierarchical porous activated carbon is a superior material in manufacturing supercapacitors. However, the hierarchical porous structure is hard to obtain from a single activation method. This work was carried out with the anticipation of producing activated carbon by reactivating corn flour with KOH. By employing the electrodes, the supercapacitor demonstrated a high discharge capacitance (151.2 F·g-1 at 1 A·g-1), and the specific capacitance is with 3.7 times more capacitance than the activated carbon only through H3PO4 activation. The mechanism of improving the electrical performance has been discussed through performing SEM, XRD, EIS, and Raman analysis. The hierarchical porous and disordered structure emerge smaller charge transfer resistance, and fast electron transfer.

Egg shell waste as an activation agent for the manufacture of porous carbon

Egg shell waste was used as an activation agent directly for the manufacture of a biomass-derived porous carbon,which possessed a surface area of 626 m2·g-1 and was rich in nitrogen,sulfur and oxygen functionalities.The activation mechanism was proposed,and the carbon showed its potential to act as an adsorbent for the adsorptive removal of various contaminants from both aqueous and non-aqueous solutions,possessing maximum adsorption capacities of 195.9,185.1,125.5 and 44.6 mg·g-1 for sulfamethoxazole,methyl orange,diclofenac sodium and dibenzothiophene,respectively.Through the utilization of egg shell waste as a sustainable activation agent,this work may help to make the widely applied biomass-derived porous carbons more economical and ecological.

Preparation of Activated Carbons from Mongolian Lignite and Sub-Bituminous Coal by a Physical Method

Preparation of activated carbons by a physical activation technique is performed using the methods of coal pyrolysis and gasification at different temperatures. As increasing pyrolysis temperature from 520°C to 700°C, the yield of activated carbons from the Khuut (KH) sub-bituminous coal is lowered, and amount of micropores increases gradually;however there is no development of mesopores by the KH coal pyrolysis. When the KH coal has a small loss during its physical activation due to difficulty and inactivity of its macrostructure decomposition, the smaller porosity is developed in the resulting carbons. The Aduunchuluun (AD) lignite is activated by pyrolysis and gasification at the highest temperature of 700°C in the present study. It is identified that the gasification of AD lignite develops well a porous structure with the highest surface area of 522 m2/g which is three times larger than that (155 m2/g) of the activated carbon produced by pyrolysis of the same lignite. The IR and SEM analysis confirm a significant difference in chemical and structural changes between the AD, KH raw coals and corresponding carbon samples in the physical activation processes.

Adsorption of phenol from aqueous solution by a hierarchical micro-nano porous carbon material

A hierarchical micro-nano porous carbon material (MNC) was prepared using expanded graphite (EG), sucrose, and phosphoric acid as raw materials, followed by sucrose-phosphoric acid solution impregnation, solidification, carbonization and activation. Nitrogen adsorption and mercury porosimetry show that mixed nanopores and micropores coexist in MNC with a high specific surface area of 1978 m2·g-1 and a total pore volume of 0.99 cm3·g-1. In addition, the MNC is found to consist of EG and activated carbon with the latter deposited on the interior and the exterior surfaces of the EG pores. The thickness of the activated carbon layer is calculated to be about one hundred nanometers and is further confirmed by scanning electron microscope (SEM) and transmission election microscope (TEM). A maximum static phenol adsorption of 241.2 mg·g-1 was obtained by using MNC, slightly higher than that of 220.4 mg·g-1 by using commercial activated carbon (CAC). The phenol adsorption kinetics were investigated and the data fitted well to a pseudo-second-order model. Also, an intra-particle diffusion mechanism was proposed. Furthermore, it is found that the dynamic adsorption capacity of MNC is nearly three times that of CAC. The results suggest that the MNC is a more efficient adsorbent than CAC for the removal of phenol from aqueous solution.

Construction of efficient active sites through cyano‐modified graphitic carbon nitride for photocatalytic CO_(2) reduction

The active site amount of photocatalysts,being the key factors in photocatalytic reactions,directly affects the photocatalytic performance of the photocatalyst.Pristine graphitic carbon nitride(g‐C_(3)N_(4))exhibits moderate photocatalytic activity due to insufficient active sites.In this study,cyano‐modified porous g‐C_(3)N_(4)nanosheets(MCN‐0.5)were synthesized through molecular self‐assembly and alkali‐assisted strategies.The cyano group acted as the active site of the photocatalytic reaction,because the good electron‐withdrawing property of the cyano group promoted carrier separation.Benefiting from the effect of the active sites,MCN‐0.5 exhibited significantly enhanced photocatalytic activity for CO2 reduction under visible light irradiation.Notably,the photocatalytic activity of MCN‐0.5 was significantly reduced when the cyano groups were removed by hydrochloric acid(HCl)treatment,further verifying the role of cyano groups as active sites.The photoreduction of Pt nanoparticles provided an intuitive indication that the introduction of cyano groups provided more active sites for the photocatalytic reaction.Furthermore,the controlled experiments showed that g‐C_(3)N_(4)grafted with cyano groups using melamine as the precursor exhibited enhanced photocatalytic activity,which proved the versatility of the strategy for enhancing the activity of g‐C_(3)N_(4)via cyano group modification.In situ diffuse reflectance infrared Fourier transform spectroscopy and theoretical calculations were used to investigate the mechanism of enhanced photocatalytic activity for CO2 reduction by cyano‐modified g‐C_(3)N_(4).This work provides a promising route for promoting efficient solar energy conversion by designing active sites in photocatalysts.

Combination of binary active sites into heterogeneous porous polymer catalysts for efficient transformation of CO_(2) under mild conditions

The transformation of CO_(2)into cyclic carbonates via atom-economical cycloadditions with epoxides has recently attracted tremendous attention.On one hand,though many heterogeneous catalysts have been developed for this reaction,they typically suffer from disadvantages such as the need for severe reaction conditions,catalyst loss,and large amounts of soluble co-catalysts.On the other hand,the development of heterogeneous catalysts featuring multiple and cooperative active sites,remains challenging and desirable.In this study,we prepared a series of porous organic catalysts(POP-PBnCl-TPPMg-x)via the copolymerization metal-porphyrin compounds and phosphonium salt monomers in various ratios.The resulting materials contain both Lewis-acidic and Lewis-basic active sites.The molecular-level combination of these sites in the same polymer allows these active sites to work synergistically,giving rise to excellent performance in the cycloaddition reaction of CO_(2)with epoxides,under mild conditions(40℃ and 1 atm CO_(2))in the absence of soluble co-catalysts.POP-PBnCl-TPPMg-12 can also efficiently fixate CO_(2)under low-CO_(2)-concentration(15%v/v N2)conditions representative of typical CO_(2)compositions in industrial exhaust gases.More importantly,this catalyst shows excellent recyclability and can easily be separated and reused at least five times while maintaining its activity.In view of their heterogeneous nature and excellent catalytic performance,the obtained catalysts are promising candidates for the transformation of industrially generated CO_(2)into high value-added chemicals.