States of graphene oxide and surface functional groups amid adsorption of dyes and heavy metal ions

Water pollution regarding dyes and heavy metal ions is crucial facing the world.How to effectively separate these contaminants from water has been a key issue.Graphene oxide(GO)promises the greenwater world as a long-lasting spotlight adsorbent material and therefore,harnessing GO has been the research hotspot for over a decade.The state of GO as well as its surface functional groups plays an important role in adsorption.And the way of preparation and structural modification matters to the performance of GO.In this review,the significance of the state of existence of stock GO and surface functional groups is explored in terms of preparation,structural modification,and adsorption.Besides,various adsorbates for GO adsorption are also involved,the discussion of which is rarely established elsewhere.

Effect of acidic surface functional groups on Cr(Ⅵ) removal by activated carbon from aqueous solution

The activated carbon with high surface area was prepared by KOH activation.It was further modified by H2SO4 and HNO3 to introduce more surface functional groups.The pore structure of the activated carbons before and after modification was analyzed based on the nitrogen adsorption isotherms.The morphology of those activated carbons was characterized using scanning electronic microscopy （SEM）.The surface functional groups were determined by Fourier transform infrared spectroscopy （FTIR）.The quantity of those groups was measured by the Boehm titration method.Cr（VI） removal by the activated carbons from aqueous solution was investigated at different pH values.The results show that compared with H2SO4,HNO3 destructs the original pore of the activated carbon more seriously and induces more acidic surface functional groups on the activated carbon.The pH value of the solution plays a key role in the Cr（VI） removal.The ability of reducing Cr（VI） to Cr（III） by the activated carbons is relative to the acidic surface functional groups.At higher pH values,the Cr（VI） removal ratio is improved by increasing the acidic surface functional groups of the activated carbons.At lower pH values,however,the acidic surface functional groups almost have no effect on the Cr（VI） removal by the activated carbon from aqueous solution.

The high catalytic activity and strong stability of 3%Fe/AC catalysts for catalytic wet peroxide oxidation of m-cresol: The role of surface functional groups and FeO_(x) particles

FeO;supported on activated carbon(AC) has been shown to be an ideal catalyst for catalytic wet peroxide oxidation(CWPO) due to its high CWPO reaction activity and stability. Although there have been some studies on the mechanism of Fe/AC catalysis in CWPO, the specific contribution of each component(surface oxygen groups and FeOxon AC) inside an Fe/AC catalyst and their corresponding reaction mechanism remain unclear, and the reaction stability of CWPO catalysts has rarely been discussed. Then the optimal CWPO catalyst in our laboratory, 3%Fe/AC, was selected.(1) By removing certain components on the AC through heat treatment, its contribution to the reaction and the corresponding reaction mechanism were investigated. With the aid of temperature-programmed desorption–mass spectrometry(TPD–MS) and the CWPO reaction, the normalized catalytic contributions of components were shown to be: 37.3%(carboxylic groups), 5.3%(anhydride), 19.3%(ether/hydroxyl),-71.4%(carbonyl groups) and 100%(FeOx),respectively. DFT calculation and EPR analysis confirmed that carboxylic groups and Fe_(2)O_(3) are able to activate the H_(2)O_(2) to generate·OH.(2) The catalysts at were characterized at different reaction times(0 h, 450 h, 900 h, 1350 h, and 1800 h) by TPD–MS and M?ssbauer spectroscopy. Results suggested that the number of carboxylic goups gradually increased and the size of paramagnetic Fe_(2)O_(3) particle crystallites gradually increased as the reactions progressed. The occurrence of strong interactions between metal oxides and AC was also confirmed. Due to these effects, the strong stability of 3%Fe/AC was further improved. Therefore, the reasons for the high activity and strong stability of 3%Fe/AC in CWPO were clearly shown. We believe that this work provides an idea of the removal of cresols from wastewater into the introduction to show the potential applications of CWPO.

Surface functional groups and redox property of modified activated carbons

一系列激活的碳(交流) 与目的作为激活代理人用 HNO3， H2O2 和蒸气被准备在交流准备过程把功能的组介绍给碳表面。激活代理人，功能的组和交流的氧化还原作用性质被温度节目解吸附作用(TPD ) 描绘的表面上的激活时间和周期的 Voltammetry (CV ) 的集中的效果。结果证明交流的内酯组与组们与 HNO3 的集中增加的激活时间，和 carboxyl 由 HNO3 增加激活。交流的羰基 / 奎宁组与激活时间和 H2O2 的集中由 H2O2 增加激活，尽管酸的组与 H2O2 的集中减少。CV 在 0 和 0.5 V 反映的氧化还原作用性质与功能的组由 TPD 描绘了的任何种氧是不同的，但是它与 SO2 催化氧化 / 氧化性质由 TPR 显示了一致。

Variations in surface functional groups, carbon chemical state and graphitization degree during thermal deactivation of diesel soot particles

The thermal deactivation of diesel soot particles exerts a significant influence on the control strategy for the regeneration of diesel particulate filters(DPFs).This work focused on the changes in the surface functional groups,carbon chemical state,and graphitization degree during thermal treatment in an inert gas environment at intermediate temperatures of 600℃,800℃,and 1000℃ and explore the chemical species that were desorbed from the diesel soot surface during thermal treatment using a thermogravimetric analyser coupled with a gas-chromatograph mass spectrometer(TGA-GC/MS).The surface functional groups and carbon chemical statewere characterized using Fourier transform infrared spectroscopy(FT-IR)and X-ray photoelectron spectroscopy(XPS).The graphitization degree was evaluated by means of Raman spectroscopy(RS).The concentrations of aliphatic C–H,C–OH,C=O,and O–C=O groups are reduced for diesel soot and carbon black when increasing the thermal treatment temperature,while the sp^(2)/sp^(3) hybridized ratio and graphitization degree enhance.These results provide comprehensive evidence of the decreased reactivity of soot samples.Among oxygenated functional groups,the percentage reduction during thermal treatment is the largest for the O–C=O groups owing to its worst thermodynamic stability.TGA-GC/MS results show that the aliphatic and aromatic chains and oxygenated species would be desorbed from the soot surface during 1000℃ thermal treatment of diesel soot.

Enhancement of gaseous mercury(Hg^0) adsorption for the modified activated carbons by surface acid oxygen function groups

This article discussed the benzoic acid activated carbons which have changed the types and content of acid oxygen-function groups on the surface of activated carbons and their effect on the adsorption for Hg^0 in simulated flue gas at 140 ℃. These surface acid oxygen function groups were identified by Boehm titration, Fourier transformation infrared spectrum, temperature programmed desorption and X-ray photoelectron spectroscopy. It indicates that the carboxyl, lactone and phenolic were formed when the benzoic acid is loaded on the surface of activated carbons. Among the surface acid oxygen function groups, the carboxyl groups enhance the adsorption capacities of Hg^0 for activated carbons to a greater extent.

Structural properties of residual carbon in coal gasification fine slag and their influence on flotation separation and resource utilization:A review

Coal gasification fine slag(FS)is a typical solid waste generated in coal gasification.Its current disposal methods of stockpil-ing and landfilling have caused serious soil and ecological hazards.Separation recovery and the high-value utilization of residual carbon(RC)in FS are the keys to realizing the win-win situation of the coal chemical industry in terms of economic and environmental benefits.The structural properties,such as pore,surface functional group,and microcrystalline structures,of RC in FS(FS-RC)not only affect the flotation recovery efficiency of FS-RC but also form the basis for the high-value utilization of FS-RC.In this paper,the characteristics of FS-RC in terms of pore structure,surface functional groups,and microcrystalline structure are sorted out in accordance with gasification type and FS particle size.The reasons for the formation of the special structural properties of FS-RC are analyzed,and their influence on the flotation separation and high-value utilization of FS-RC is summarized.Separation methods based on the pore structural characterist-ics of FS-RC,such as ultrasonic pretreatment-pore-blocking flotation and pore breaking-flocculation flotation,are proposed to be the key development technologies for improving FS-RC recovery in the future.The design of low-cost,low-dose collectors containing polar bonds based on the surface and microcrystalline structures of FS-RC is proposed to be an important breakthrough point for strengthening the flotation efficiency of FS-RC in the future.The high-value utilization of FS should be based on the physicochemical structural proper-ties of FS-RC and should focus on the environmental impact of hazardous elements and the recyclability of chemical waste liquid to es-tablish an environmentally friendly utilization method.This review is of great theoretical importance for the comprehensive understand-ing of the unique structural properties of FS-RC,the breakthrough of the technological bottleneck in the efficient flotation separation of FS,and the expansion of the field of the high value-added utilization of FS-RC.

Hard-carbon hybrid Li-ion/metal anode enabled by preferred mesoporous uniform lithium growth mechanism

To achieve high energy density in lithium batteries,the construction of lithium-ion/metal hybrid anodes is a promising strategy.In particular,because of the anisotropy of graphite,hybrid anode formed by graphite/Li metal has low transport kinetics and is easy to causes the growth of lithium dendrites and accumulation of dead Li,which seriously affects the cycle life of batteries and even causes safety problems.Here,by comparing graphite with two types of hard carbon,it was found that hybrid anode formed by hard carbon and lithium metal,possessing more disordered mesoporous structure and lithophilic groups,presents better performance.Results indicate that the mesoporous structure provides abundant active site and storage space for dead lithium.With the synergistic effect of this structure and lithophilic functional groups(–COOH),the reversibility of hard carbon/lithium metal hybrid anode is maintained,promoting uniform deposition of lithium metal and alleviating formation of lithium dendrites.The hybrid anode maintains a 99.5%Coulombic efficiency(CE)after 260 cycles at a specific capacity of 500 m Ah/g.This work provides new insights into the hybrid anodes formed by carbon-based materials and lithium metal with high specific energy and fast charging ability.

Role of biochar surface characteristics in the adsorption of aromatic compounds:Pore structure and functional groups

Biochar(BC)are widely used as highly efficient adsorbents to alleviate aromatics-based contaminants due to their ease of preparation,wide availability,and high sustainability.The surface properties of BCs usually vary greatly due to their complex chemical constituents and different preparation processes and are reflected in the values of parameters such as the specific surface area(SSA),pore volume/size,and surface functional groups(SFGs).The effects of SSA and pore volume/size on the adsorption of aromatics have been widely reported.However,the corresponding mechanisms of BC SFGs towards aromatics adsorption remains unclear as the compositions of the SFGs are usually complex and hard to determine.To address in this gap in the literature,this review introduces a new perspective on the adsorption mechanisms of aromatics.Through collecting previously-reported results,the parameters log P(logarithm of the Kow),polar surface area,and the positive/negative charges were carefully calculated using Chem Draw3D,which allowed the hydrophobicity/hydrophilicity properties,electron donor-acceptor interactions,Hbonding,and electrostatic interactions between SFGs and aromatics-based contaminates to be inferred intuitively.These predictions were consistent with the reported results and showed that tailor-made BCs can be designed according to the molecular weights,chemical structures,and polarities of the target aromatics.Overall,this review provides new insight into predicting the physicochemical properties of BCs through revealing the relationship between SFGs and adsorbates,which may provide useful guidance for the preparing of highly-efficient,functional BCs for the adsorption of aromatics.

Atomic defects,functional groups and properties in MXenes

MXenes,a new family of functional two-dimensional(2 D) materials,have shown great potential for an extensive variety of applications within the last decade.Atomic defects and functional groups in MXenes are known to have a tremendous influence on the functional properties.In this review,we focus on recent progress in the characterization of atomic defects and functional group chemistry in MXenes,and how to control them to directly influence various properties(e.g.,electron transport,Li^(+) adsorption,hydrogen evolution reaction(HER) activity,and magnetism) of 2 D MXenes materials.Dynamic structural transformations such as oxidation and growth induced by atomic defects in MXenes are also discussed.The review thus provides perspectives on property optimization through atomic defect engineering,and bottom-up synthesis methods based on defect-assisted homoepitaxial growth of MXenes.

First principles study on geometric and electronic properties of two-dimensional Nb_(2)CT_(x) MXenes

MXenes are a new type of two-dimensional carbides with rich physical and chemical properties. The physics of MXenes, and thus the applications, are dominated by surface functional groups. Herein, the effects of different terminations(O,S, Se, Te) on the geometric and electronic properties of Nb_(2)C MXenes were studied via density functional theory(DFT)calculations. Three adsorption sites were examined to determine the most stable configurations. The results showed that both the types and the positions of surface functional groups influence the geometric stability and physical characters of Nb_(2)C. The S and Se terminations make the Nb_(2)C MXenes to be semiconductor, while Nb_(2)C MXenes with other terminations(O, Te) are conductor. The electron location function, density of states, Bader charge distribution, and the projected crystal orbital Hamilton population were conducted to explain the origin of adsorption stability and electronic nature difference. Our results provide a fundamental understanding about the effects of surface terminations on the intrinsic stability and electronic properties of Nb_(2)C MXenes.

Influence of N doping and the functional groups of graphene on a RGO/TiO2 composite photocatalyst

Reduced graphene oxide(RGO)assisted TiO2 composite photocatalysts have attracted increased attention because of their high photocatalytic performance under both UV-and visible-light irradiation.However,the corresponding properties under the long wavelength irradiation is far from expected.In this study,a series of RGO samples with well-designed N impurity and optimized surface functional groups are prepared and employed during hybridization with TiO2(named N-RGO/TiO2).The coupling between the doped N atoms and surface functional groups is analyzed based on the resulting photocatalytic performances,and the specific mechanism is revealed by the EPR,IR and lifetime of the photoinduced electrons.After comparing the corresponding performances of the RGO/TiO2 and RGO/N-TiO2 specimens,the results show that the surface functional groups of the RGO serve as a precondition to achieveπ-d coupling between the graphene basal plane and TiO2 nanoparticles,while N atoms in the RGO enhance the resulting photoactivity under a long wavelength range(>510 nm).The findings provide a potential approach to promote the photocatalytic properties of graphene-based composite photocatalysts with the low-energy incident photons.

Acid/Base Treatment of Monolithic Activated Carbon for Coating Silver with Tunable Morphology

Silver coatings on the exterior surface of monolithic activated carbon（MAC） with different morphology were prepared by directly immersing MAC into [Ag（NH3）2]NO3 solution. Acid and base treatments were employed to modify the surface oxygenic groups of MAC, respectively. The MACs＇ Brunauer-EmmettTeller（BET） surface area, surface groups, and silver coating morphology were characterized by N2 adsorption, elemental analysis（EA）, X-ray photoelectron spectroscopy（XPS）, and scanning electron microscopy（SEM）, respectively. The coating morphology was found to be closely related to the surface area and surface functional groups of MAC. For a raw MAC which contained a variety of oxygenic groups, HNO3 treatment enhanced the relative amount of highly oxidized groups such as carboxyl and carbonates, which disfavored the deposition of silver particles. By contrast, Na OH treatment significantly improved the amount of carbonyl groups, which in turn improved the deposition amount of silver. Importantly, lamella silver was produced on raw MAC while Na OH treatment resulted in granular particles because of the capping effect of carbonyl groups. At appropriate [Ag（NH3）2]NO3 concentrations, silver nanoparticles smaller than 100 nm were homogeneously dispersed on Na OH-treated MAC. The successful tuning of the size and morphology of silver coatings on MAC is promising for novel applications in air purification and for antibacterial or aesthetic purposes.

Surface carboxyl groups enhance the capacities of carbonaceous oxygen electrodes for aprotic lithiumoxygen batteries: A direct observation on binder-free electrodes

In order to achieve the high capacities of carbonaceous oxygen diffusion electrodes for aprotic lithiumoxygen batteries(Li-O2 batteries),most efforts currently focus on the design of rational porous architectures.Only few works study the surface chemistry effect that might be a critical factor influencing the capacities of carbonaceous electrodes.In addition,the surface chemistry effect is very difficult to be studied in composite electrodes due to the influences of binders and additives.Herein,we propose chemically activated carbon cloth(CACC) as an ideal model to investigate the effect of surface functional groups on the discharge capacities of carbonaceous oxygen electrodes for Li-O2 batteries.The intrinsic surface chemistry effect on the performance of carbonaceous cathode is directly observed for the first time without the influences of binders and additives.Results indicate that the surface carboxyl groups introduced by the chemical treatment not only function as the appropriate nucleation sites for Li2 O2 but also induce the formation of toroid-like Li2 O2.Thus,the surface carboxyl modification enhances the discharge capacities from 0.48 mAh/cm^2 of pristine carbon cloth to 1.23 mAh/cm^2 of CACC.This work presents an effective way to further optimize the carbonaceous oxygen electrodes via surface functional group engineering.

Surface chemistry engineering and the applications of MXenes

MXenes have captured extensive attention in various fields by virtue of unique hydrophilicity,high conductivity and tunable surface terminations.In this review,the state-of-the-art progresses of designing functional MXenes have been summarized.Firstly,the synthesis methods of MXenes are summarized and classified into HF etching,in-situ HF etching and fluoride-free etching approaches based on the effect on the surface chemistry of MXenes.Secondly,the factors that affect the surface termination groups are discussed,including synthesis methods,heat treatment temperature and atmosphere.Thirdly,this review gives an overview of the synthetic routes of functional MXenes including termination modification by synthesis methods and heat treatment,heteroatom(N,S,or P)doping,cation and organic molecule intercalation and hybridization with polymer,which inhibit restacking and increase active sites for intrinsically enhancing the inherent physical and chemical properties of MXenes.Finally,the applications with respect to energy storage and conversion,catalysis,sensors,electromagnetic interference shielding and microwave absorption of functional MXenes are introduced.Additionally,the critical challenges and development prospects of functional MXenes are also highlighted.