Oxygen-containing Functionalities Research Articles

Inherent water in green pine needles and cypress leaves induces self-activation in microwave pyrolysis

The response of water to microwaves creates the possibility of activating green waste for the generation of porous biochar with inherent water. This hypothesis is verified herein through the microwave pyrolysis of green and dried pine needles and cypress leaves at 500 to 800 °C. The results indicate that the inherent water in the green samples induce steam reforming or gasification, thereby forming more gases at the expense of biochar and organics, such as light and heavy phenolics in bio-oil. The intensive gasification induced by the inherent water of green pine needles effectively promotes the pore development of biochar at 800 °C (805.9 versus 360.4 m2/g from the dried sample) and the adsorption of phenol (50.3 versus 34.8 mg/g from the dried sample). A similar result is observed for the pyrolysis of cypress leaves at 800 °C (452.1 m2/g from the green samples versus 110.8 m2/g from the dried samples). A lower temperature (i.e., 500 °C) with insufficient gasification results in no marked difference in pore development. Accelerated gasification with steam leads to the excessive removal of aliphatic organics but also introduces more oxygen in the biochar, making it more hydrophilic with a more fragmented surface. Nevertheless, potential local hot spots, if any, do not lead to the decomposition of inorganics, such as CaCO3, in the pyrolysis of green samples, while the pyrolysis of dried cypress does. The pyrolysis in in-situ infrared shows that 500 °C is required to effectively destruct hydrogen bonds in the green samples and the inherent water promotes the formation of more oxygen-containing functionalities but not aromatization.

Thiol-ene Click Chemistry Synthesis of L-Cysteine-Grafted Graphene Oxide As a New Corrosion Inhibitor for Q235 Steel in Acidic Environment.

l-cysteine, as an eco-friendly and nontoxic corrosion inhibitor, was directly covalently linked to the carbon/carbon double bonds of the GO flakes by a thiol-ene click reaction to avoid decreasing the number of hydrophilic oxygen-containing polar functionalities. The corrosion inhibition performances of Cys-GO toward Q235 steel (QS) in diluted hydrochloric acid were studied by electrochemical methods. The corrosion was a charge transfer-controlled process, and Cys-GO manifested as a mixed-type corrosion inhibitor. The corrosion inhibition efficiency (η) for QS showed a first-increase-and-then-decrease trend with increasing Cys-GO concentrations. The optimum concentration of Cys-GO was 15 mg L-1, and the according η value was up to 90%. The Cys-GO adsorbed on the QS surface to form a protective barrier was responsible for the efficient corrosion inhibition. Langmuir adsorption isotherm model was fitted well with the experiment data, indicating a monolayer adsorption. Furthermore, the coordinate covalent bonds, π-back-donation effect, and electrostatic attraction were responsible for the Cys-GO adsorption on the QS surface.

Enhancing Graphene Nanoplatelet Reactivity through Low-Temperature Plasma Modification.

Graphene-based materials have great potential for applications in many fields, but their poor dispersion in polar solvents and chemical inertness require improvements. Low-temperature plasma allows the precise modification of materials, improving the physicochemical properties of the surface and thus creating the possibility of their potential use. Plasma treatment offers the possibility of introducing oxygen functional groups simply, rapidly, and in a controlled way. In this work, a systematic investigation of the effect of plasma modification on graphene nanoplatelets has been carried out to determine the optimal plasma parameters, especially the exposure time, for introducing the highest amount of oxygen functional groups on a surface. Different gases (O2, CO2, air, Ar, and C2H4) were used for this purpose. The chemical nature of the introduced oxygen-containing functionalities was characterized by X-ray photoelectron spectroscopy, and the structural properties of the materials were studied by Raman spectroscopy. The plasma-induced changes have been shown to evolve as the surface functionalities observed after plasma treatment are unstable. The immersion of the materials in liquids was carried out to check the reactivity of carbons in postplasma reactions. Stabilization of the material's surface after plasma treatment using CH3COOH was the most effective for introducing oxygen functional groups.

Oxidative pyrolysis of poplar sawdust: Probing the influence of oxidation reactions on property of biochar

Partial oxidation of some organics is desirable in some scenarios for compensation of the heat required for pyrolysis, which, however, impacts not only composition of bio-oil but also possibly property of biochar. This was investigated herein by oxidative pyrolysis of poplar sawdust from 300 to 600 °C and further analysis of the pyrolytic products, especially biochar. The results showed that O2 could oxidize some organics on surface of biochar, forming more volatiles below 400 °C. Above this temperature the excessive oxidation of the light and heavy organics with π-conjugated structures in bio-oil dominated, producing more gases. Weight loss of biochar from oxidation of organics on its surface was only remarkable at 300 °C, while some weight gain was observed from introduction of additional oxygen-containing functionalities from the oxidation. The removal of aromatic structures on biochar at 500 or 600 °C via oxidation was rather difficult. However, the oxidation reactions did make the biochar oxygen-rich but hydrogen-deficient, which, in overall, improved thermal stability and comprehensive combustion performance of the biochar. Additionally, oxygen presence enhanced aromatic degree of biochar by increasing regularity of (100) facet of carbon crystals while narrowing interplanar spacing of (002) facets. The oxygen-rich nature also made the biochar from the oxidative pyrolysis more hydrophilic while the removal of some organics via oxidation promoted development of the pore structures.

Catalytic conversion of volatiles over homologous char: Distinct interaction patterns at different temperatures

Char produced at specific pyrolysis temperatures has specific surface properties, which is also expected to have specific interaction patterns with volatiles produced at the same temperature. In this study, the char produced at varied temperatures was used for catalyzing conversion of homogenous volatiles generated at the same temperature. The aim was to explore the change of properties of char catalyst via volatiles-char interaction, which was almost equivalent to the evolution of property of char in pyrolysis. The results suggested that the char-300 (the number refers to temperature (°C) for production of char) and char-450 retained abundant oxygen-containing functionalities, rendering them superior activity for cracking of aliphatics and aromatics, producing less bio-oil with a lower abundance of π-conjugated structures but more gases (especially over char-450, increased by 57.8%). Char-600 and char-750, with a lower abundance of oxygen-containing functionalities, were not that active for cracking or interaction with volatiles, and their properties were also not changed that much. In comparison, the spent char-300 and char-450 experienced remarkable dehydrogenation and deoxygenation via interaction with volatiles, resulting in overall net weight loss, increased carbon content as well as enhanced thermal stability, aromatic degree, and carbon crystallinity. The biggest change of char-600 and char-750 could be the filling of pores with volatiles-derived deposits. The characterization of catalytic pyrolysis with in-situ IR technique also confirmed that the char-300 showed higher capability than char-750 for catalyzing conversion –OH and CO via varied reaction routes.

Enhanced abundance of oxygen-containing intermediates from pre-oxidation of poplar sawdust facilitates generation of porous structures in activation with phosphoric acid

Pretreatment of biomass in oxidative atmosphere could induce partial oxidation of organic components on surface of biochar, which might affect evolution of pore structures in subsequent activation of biochar. This was investigated herein by pretreatment of sawdust at 150 to 300 °C in an air or nitrogen flow and the followed activation of the resulting biochar with phosphoric acid. The results indicated that the oxidation in the pretreatment in air became substantial at 250 °C, reducing the yield of biochar, crystallinity of cellulose while introducing abundant oxygen-containing functionalities in form of OH, COC, CO, etc. Some of these oxygen-containing species even can be reserved in the activated carbon (AC) formed, making the oxygen-rich AC with high hydrophilicity. More importantly, these abundant oxygen-containing functionalities were beneficial for the subsequent activation with phosphoric acid for creating developed pore structures (1314.3 m2g−1 of AC-250-air versus 1056.5 m2g−1 of AC-250-N2). This resulted in superior adsorption capacity towards tetracycline over AC-250-air. The in-situ IR characterization suggested that abundant oxygen-containing species bearing ester/carboxyl functionalities were generated during activation of the sawdust pretreated in air, which played essential roles in generation of especially micropores. The deficiency of these oxygen-containing species in activation of the sawdust pretreated in nitrogen negatively affected development of pores.

Oil palm waste-derived reduced graphene oxide (rGO) for dynamic adsorption of dye in a fixed-bed system

This study focuses on investigating the dynamic adsorption of Rhodamine B (RhB) from reduced graphene oxide (rGO) derived from oil palm waste. The synthesis of rGO from palm kernel shell (PKS) was achieved through double oxidation and carbonization method, resulting in a yield of 73.5 wt%. The reduction of oxygen-containing functionalities process using PKS was confirmed by FTIR spectroscopy, microscopic evaluation, and X-ray diffraction analyses. Laboratory-scale fixed-bed experiments were conducted with various process parameters. Both PKS and rGO were used as adsorbents, and a comparison was made based on breakthrough curve analysis, adsorption capacity and percentage removal of dye. The adsorption kinetics of RhB on PKS and rGO were best described by the non-linear Yoon-Nelson model, with a high adsorption capacity of 88.32 mg/g and 195.24 mg/g respectively. Using both PKS and rGO, the maximum adsorption capacity was observed when using 10 cm bed depth column, inlet dye concentration of 5 mg/L, flow rate of 12 mL/min and pH of 7. PKS exhibited good dye removal with an efficiency of 66.54%. Meanwhile, the exothermic behavior highlighted the potential of utilizing rGO for maximum dye removal, achieving an efficiency of 90.35%. This study justifies rGO as a cost-effective superior dye removal adsorbent, providing new prospect for large-scale dye removal.

Performance analysis of hydrochar derived from catalytic hydrothermal carbonization in the multicomponent emerging contaminant systems: Selectivity and modeling studies

In this work, as an alternative to pyrochar, catalytic hydrothermal carbonization has been employed to synthesize hydrochar to eliminate emerging contaminants in multicomponent systems. The hydrochar has been synthesized using a single step catalytic hydrothermal carbonization at low temperature (200 °C) without any secondary activation with high specific surface area and very good adsorption efficiency for the removal of emerging contaminants. The synthesized hydrochar (HC200) was characterized using various analytical techniques and found to have porous structure with 114.84 m2.g−1 of specific surface area and also contained various oxygen-containing functionalities. The maximum adsorption efficiencies of 92.4 %, 85.4 %, and 82 % were obtained for ibuprofen, sulfamethoxazole, and bisphenol A, respectively. Humic acid, a naturally occurring organic compound had a negligible effect on the adsorption of the selected contaminants. The hydrochar's selectivity towards the emerging contaminants in binary and ternary multicomponent systems was in the order of ibuprofen > sulfamethoxazole > bisphenol A.

Preparation of Graphene Oxide Hydrogels and Their Adsorption Applications toward Various Heavy Metal Ions in Aqueous Media

Graphene oxide is a two-dimensional material that has been extensively studied in various fields due to its good mechanical properties, water dispersibility, and a large number of oxygen-containing functionalities on its surface. In this study, graphene oxide powder was prepared using graphite powder to take advantage of its large specific surface area and abundance of oxygen-containing functional groups. The graphene oxide powder was cross-linked with acrylic acid and acrylamide and polymerized to produce graphene oxide hydrogels, which were used to adsorb four metal ions including Cu(II), Pb(II), Zn(II), and Cd(II) from aqueous solutions. The adsorption performance of the graphene oxide hydrogels was investigated at different pHs, temperatures, initial metal ion concentrations, and competition principles, as well as their adsorption and desorption after three repeated adsorption–desorption experiments. It was found that the graphene oxide hydrogels exhibited good adsorption performance for all four metal ions under different conditions. The graphene oxide hydrogels for the adsorption of Cu(II), Pb(II), Zn(II), and Cd(II) ions were best fitted using the Langmuir monolayer adsorption model and the quasi-secondary reaction kinetic model. Good adsorption was achieved for all four metal ions under different competing adsorption principles. After three adsorption–desorption cycles, the adsorption capacity of the graphene oxide hydrogels for all four metal ions remained at 88% and above. These results indicate that graphene oxide hydrogels are a stable, efficient, low-cost, and reusable adsorbent material for the treatment of metal ions in solution.

Vacuum ultraviolet-induced surface modification of polyoxymethylene plates for photo-activation bonding

The surface photoactivation technique using vacuum ultra-violet (VUV) light at 172 nm in wavelength has been applied for adhesive-free bonding of polyoxymethylene (POM) plates. The POM surfaces were photochemically modified via VUV light irradiation in dry air conditions, resulting in the formation of oxygen-containing functionalities. The POM plates were successfully bonded with a practical bonding strength below the melting point. The maximum bonding strength was obtained at an irradiation time of 60 min, while a longer irradiation time resulted in lower bonding strength. Surface morphologies of the photoactivated and fractured POM surfaces were observed by a laser scanning microscope. Due to the VUV irradiation, numerous cracks were formed on the POM surfaces. The fractured surface shows that a cohesive failure occurs at the bonding interface. Atomic force microscopy was used to observe the cross-sectional images of the bonding samples. Around 10 μm width, significant phase contrast between the bonding interface and bulk POM indicates the different mechanical properties, due to VUV irradiation. The modified POM surfaces adhered through thermocompression, and the mechanical interlocking and entanglement of POM molecules can result in successful bonding.

Balanced anchoring sites and volatile matter in biochar render Ni/biochar with higher metal dispersion and superior activity in hydrogenation of vanillin

Metal/carbon catalysts could be prepared via simple calcination of biochar impregnated with salt of metal precursors. Abundance of oxygen-containing functionalities on biochar affects dispersion of nickel via influencing availability of anchoring sites for nickel ions in impregnation step. Biochar with high content of volatile matter tended to have more oxygen-containing species, but the volatiles released in calcination of Ni/biochar could experience secondary condensation, forming carbonaceous deposit and covering nickel sites. Therefore, the balanced distribution of oxygen-containing functionalities and volatile matter in biochar on dispersion of nickel were investigated via preparation of Ni/biochar catalysts with biochar support obtained at varied pyrolysis temperature (200, 300, 400 and 500 °C). The results indicated that the calcination of Ni/biochar-200 with biochar produced via pyrolysis at 200 °C encapsulated nickel from the deposit of secondary condensation of the volatiles, while the lack of abundance of O-containing species of biochar-400 and biochar-500 led to the growth of nickel species large crystals in their supported catalysts. In comparison, Ni/biochar-300 showed the highest dispersion of nickel and thus the highest activity for hydrogenation of vanillin to produce 2-methoxy-4-methylphenol (yield: 89.4%). The in-situ IR characterization of functionalities of biochar versus temperature and residence time indicated that the pyrolysis at 300 °C enhanced formation of –OH groups, the main anchoring sites of nickel ions. Nonetheless, abundant C = O at 400 °C and developed aromatic ring structures at 500 °C were not effective for dispersion of nickel species.

Importance of oxygen-containing functionalities and pore structures of biochar in catalyzing pyrolysis of homologous poplar

Biochar and bio-oil are produced simultaneously in one pyrolysis process, and they inevitably contact and may interact, influencing the composition of bio-oil and modifying the structure of biochar. In this sense, biochar is an inherent catalyst for pyrolysis. In this study, in order to investigate the influence of functionalities and pore structures of biochar on its capability for catalyzing the conversion of homologous volatiles in bio-oil, three char catalysts (600C, 800C, and 800AC) produced via pyrolysis of poplar wood at 600 or 800 °C or activated at 800 °C, were used for catalyzing pyrolysis of homologous poplar wood at 600 °C, respectively. The results indicated that the 600C catalyst was more active than 800C and 800AC for catalyzing cracking of volatiles to form more gas (yield increase by 40.2%) and aromatization of volatiles to form more light or heavy phenolics, due to its abundant oxygen-containing functionalities acting as active sites. The developed pores of the 800AC showed no such catalytic effect but could trap some volatiles and allow their further conversion via sufficient aromatization. Nevertheless, the interaction with the volatiles consumed oxygen on 600C (decrease by 50%), enhancing the aromatic degree and increasing thermal stability. The dominance of deposition of carbonaceous material of a very aromatic nature over 800C and 800AC resulted in net weight gain and blocked micropores but formed additional macropores. The in situ diffuse reflectance infrared Fourier transform spectroscopy characterization of the catalytic pyrolysis indicated superior activity of 600C for removal of –OH, while conversion of the intermediates bearing CO was enhanced over all the char catalysts.

Preparation of graphitic foil with high thermal conductivity using Vitamin C as reductant and binder

In the face of increased heat dissipation requirements of high-power electronic devices, the fabrication of graphitic foil with high thermal conductivity is urgently needed. In this work, graphitic foil with the thickness ranging from 424 to 900 μm is innovatively prepared by blade coating, hot-pressing, and graphitization process through solution-derived graphene oxide (GO), employing Vitamin C (VC) as reductant and binder. VC amount is optimized, the acting mechanism of VC is clarified, and the morphology and structure evolution of GO film are extensively investigated. The results indicate that VC can mildly reduce the oxygen-containing function group of GO, and the cross-linked derivatives of VC can effectively fuse the multilayer reduced graphene oxide (rGO) films and regulate the microstructure of graphitic foil. When the VC/GO mass ratio is 1, the prepared graphitic foil with a thickness of 680 µm has the best thermal diffusion ability and mechanical strength. It has a high thermal conductivity of 1042 W m−1 K−1 and tensile strength of 42.05 MPa. The thermal diffusion ability, expressed as h × K value, reaches as high as 0.708 W K−1. This study provides a pioneering strategy for constructing advanced thermal conductive materials.

Synthesis effect on surface functionalized Ti3C2Tx MXene supported nickel oxide nanocomposites with enhanced specific capacity for supercapacitor application

Rich surface functionalization and active electrolyte-accessible supercapacitors are considered promising tools for enhanced energy storage capacity due to their high specific capacity and simple construction. One of the challenges in technical applications of recently developed MXene is that it causes phase transition and structural decomposition over time without delamination. Thus, a simple but effective method for increasing the stability of exfoliated MXene (Ti3C2Tx) by passivating exposed edges with Tetramethyl Ammonium Hydroxide (TMAOH) has been adopted here. In this work, we performed this delaminated MXene (DLMX) supported Nickel oxide (NiO) by three different synthesizing routes for composite preparation which have been thoroughly discussed. Bath Sonication assisted DLMX/NiO was found to increase oxygen-containing surface functionalities, surface area, and uniform delivery of partner composite, enhancing the electrochemical properties compared to Solvothermal and in situ-delamination synthesis. At a current density of 1 A/g, the fabricated electrode material exhibited a maximum capacity of 770C/g. After 3500 cycles a remarkable cycling performance of 97.2 % capacity retention and reached 88.1 % after 5000 cycles at 8 A/g current density. The as-assembled supercapacitor device has an energy density of up to 73 Wh kg−1 and a power density of 900 W kg−1 signifying an excellent device prospect, making them more practicable for marketable devices for advanced energy storage applications.

Effects of Torrefaction Pretreatment on the Structural Features and Combustion Characteristics of Biomass-Based Fuel.

Wheat straw, a typical agricultural solid waste, was employed to clarify the effects of torrefaction on the structural features and combustion reactivity of biomass. Two typical torrefaction temperatures (543 K and 573 K), four atmospheres (argon, 6 vol.% O2, dry flue gas and raw flue gas) were selected. The elemental distribution, compositional variation, surface physicochemical structure and combustion reactivity of each sample were identified using elemental analysis, XPS, N2 adsorption, TGA and FOW methods. Oxidative torrefaction tended to optimize the fuel quality of biomass effectively, and the enhancement of torrefaction severity improved the fuel quality of wheat straw. The O2, CO2 and H2O in flue gas could synergistically enhance the desorption of hydrophilic structures during oxidative torrefaction process, especially at high temperatures. Meanwhile, the variations in microstructure of wheat straw promoted the conversion of N-A into edge nitrogen structures (N-5 and N-6), especially N-5, which is a precursor of HCN. Additionally, mild surface oxidation tended to promote the generation of some new oxygen-containing functionalities with high reactivity on the surface of wheat straw particles after undergoing oxidative torrefaction pretreatment. Due to the removal of hemicellulose and cellulose from wheat straw particles and the generation of new functional groups on the particle surfaces, the ignition temperature of each torrefied sample expressed an increasing tendency, while the Ea clearly decreased. According to the results obtained from this research, it could be concluded that torrefaction conducted in a raw flue gas atmosphere at 573 K would improve the fuel quality and reactivity of wheat straw most significantly.

Universal Strategy for Reversing Aging and Defects in Graphene Oxide for Highly Conductive Graphene Aerogels.

The production of highly stable, defect-free, and electrically conducting 3D graphene structures from graphene oxide precursors is challenging. This is because graphene oxide is a metastable material whose structure and chemistry evolve due to aging. Aging changes the relative composition of oxygen functional groups attached to the graphene oxide and negatively impacts the fabrication and properties of reduced graphene oxide. Here, we report a universal strategy to reverse the aging of graphene oxide precursors using oxygen plasma treatment. This treatment decreases the size of graphene oxide flakes and restores negative zeta potential and suspension stability in water, enabling the fabrication of compact and mechanically stable graphene aerogels using hydrothermal synthesis. Moreover, we employ high-temperature annealing to remove oxygen-containing functionalities and repair the lattice defects in reduced graphene oxide. This method allows obtaining highly electrically conducting graphene aerogels with electrical conductivity of 390 S/m and low defect density. The role of carboxyl, hydroxyl, epoxide, and ketonic oxygen species is thoroughly investigated using X-ray photoelectron and Raman spectroscopies. Our study provides unique insight into the chemical transformations occurring during the aging and thermal reduction of graphene oxide from room temperature up to 2700 °C.

Effect of oxidation degree on photoactivity, physicochemical properties and oxidative potential changes of graphene-based materials under visible light irradiation

Graphene-based materials are subject to photochemical process when releasing into the environment. In this study, three kinds of graphene-based materials, graphene oxide (GO), soot and graphene (G), were selected to investigate their photoinduced changes of properties and the corresponding reasons. GO underwent reduction-dominant disproportionation, resulting in less oxygen-containing function groups (OFGs) and higher percentage of carbon-centered persistent free radicals (PFRs). Different kinds of soot particles all experienced self-oxidation, expressed as more OFGs, defects and carbon-centered PFRs adjacent to oxygen atom. Oxidative potential (OP) tested by DTT activity showed a decrease in GO but an increase in soot, agreeing with their changes of physicochemical properties. G remained almost unchanged in terms of both physicochemical properties and OP. Photoactivity measured by the productivity of photogenerated electron-hole pair and reactive oxygen species was responsible for above changes and correlated with the inner carbonaceous core. Carbonaceous core can behave as a photocatalyst to initiate photocatalytic reaction, and its oxidation degree (O/C ratio and OFGs content) determines the photoactivity. The relationship among the physicochemical properties, OP, photoactivity and inner microstructure found in this paper will help for better understanding of the environmental behavior and health effects of graphene-based materials.

Adsorption and desorption characteristics of heavy metals onto conventional and biodegradable plastics

Biodegradable plastics have been widely used to replace conventional plastics to minimize environmental impacts of plastic packaging. However, before biodegradable plastics decompose in the environment, they could pose a threat to terrestrial and aquatic creatures by acting as vectors of contaminants in the food chain. In this study, conventional plastic bags (CPBs) made of polyethylene and biodegradable plastic bags (BPBs) made of polylactic acid were examined for their heavy metal adsorption. Effects of solution pHs and temperatures on adsorption reactions were investigated. Because of a larger BET surface area, presence of oxygen-containing function groups, and smaller crystallinity, the heavy metal adsorption capacities of BPBs are significantly larger than those of CPBs. Among Cu (up to 791.48 mg⋅kg−1), Ni (up to 60.88 mg⋅kg−1), Pb (up to 1414.58 mg⋅kg−1), and Zn (up to 295.17 mg⋅kg−1), Pb and Ni show the largest and the lowest extents of adsorption onto the plastic bags, respectively. In the different waterbodies in nature, Pb adsorption on the CPBs and the BPBs were 318.09–379.91 and 528.41–764.22 mg⋅kg−1, respectively. Consequently, Pb was selected as the target contaminant in the desorption experiments. After Pb was adsorbed onto the CPBs and the BPBs, Pb could be completely desorbed and released into simulated digestive systems in 10 h. In conclusion, BPBs could be potential vectors of heavy metals, and their suitability as a substitute for CPBs must be thoroughly investigated and confirmed.

Activation of cellulose with CO2 and/or H2O: Evolution of functionalities of the biochar and environmental impacts

CO2 and H2O are two important activators in production of activated carbon (AC) via physical activation method. They could oxidize the carbonaceous species in biochar or biomass via varied mechanisms and might also impact environments as well as the pore structures and evolution of functionalities of AC in different ways. In this study, the activations of the biochar from pyrolysis of cellulose with H2O, CO2 or mixed H2O/CO2 were performed. The results demonstrated that H2O as an activator led to higher weight loss than that of CO2 during the activation, originating from its higher efficiency for oxidation of the aliphatic structures in biochar to –OH and their further removal via deoxygenation or dehydration. Activation with CO2 made the AC more oxygen-rich, due to the retainment of abundant oxygen-containing functionalities, which suppressed further oxidation of carbon species and led to formation of main micropores. The higher capability of H2O for deoxygenation made the AC more carbon-rich with much more developed pore structures as well as higher proportion of mesopores and thus the superior capability for adsorption of phenol. In addition, during the activation in either CO2 or H2O, the unsaturated aldehyde/ketone and C-O-C structures was thermally more stable than lactones, saturated aliphatic acids and aliphatic aldehydes. The life cycle analysis (LCA) suggested that CO2 activation showed lower impact on environment by reducing emissions and consumption of fossil fuel.

Investigation of property of biochar in staged pyrolysis of cellulose

Pyrolysis involves heating of a feedstock from room temperature in an oxygen-deficient atmosphere, during which the heating at low temperature could potentially change the structure of feedstock and impacted the subsequent pyrolysis. In this study, the initial torrefaction of cellulose at 170, 260 and 350 °C and the subsequent pyrolysis at 600 °C was conducted, aiming to probe effect of the low-temperature pretreatment on evolution of the pyrolysis products, especially biochar. The results showed that the cellulose crystals could be partially destroyed at 260 °C and completely removed at 350 °C, and meanwhile aromatization reactions took place. This favored the formation of gases through further aromatization in the pyrolysis at 600 °C, but generated less light organics, especially for the pretreatment at 350 °C. The pretreatment at 260 °C, however, facilitated formation of anhydrate sugars and organics with π-conjugated structures. In addition, the torrefaction also enhanced the graphitization degree of biochar obtained at 600 °C through promoting the deoxygenation reactions, generating the biochar with higher C/O ratio, higher heating value, higher thermal stability and hydrophobicity. Besides, the torrefaction also significantly reduced formation of the reaction intermediates with aliphatic structures and the oxygen-containing functionalities such as -OH, CO and C-O-C in/on the biochar.