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Due to the high porosities, large surface areas, insolubilities in solutions, and unique structural and morphological structures, porous materials are utilized in various application areas such as energy conversion and storage, wastewater treatment, adsorption, catalysis and photocatalysis. In this study, activated carbons (QCACs), one type of porous materials, were synthesized from Quercus cerris acorn shells by using ZnCl2 chemical activation under various production conditions. The effects of carbonization temperature, carbonization period, and impregnation ratios on the yields, surface areas, pore developments, and N2 adsorption–desorption isotherms of activated carbons obtained were investigated in detail. The highest surface area (1751.61 m2/g) was reached when utilized at the impregnation ratio of 2.0 at 500 ℃ for 90 min. The total pore volume of QCAC increased with increasing impregnation ratio, however the micropore volume of QCAC reduced. It was found from the pore distribution data that QCACs contained mostly narrow mesopores and a little amount of micropores. Also, N2 adsorption–desorption isotherm data revealed that QCACs produced under different conditions were usually mesopore structures, and the pores were narrow slit-shaped. Moreover, the data provided from SEM, FTIR, Boehm titration, and elemental analysis gave more characterization information about QCACs synthesized. [ABSTRACT FROM AUTHOR]

• Frame resistant polyacrylonitrile (PAN) fiber activation with zinc chloride. • Effective quaternized nitrogen (N-Q) introduction on carbon surface. • Transformation of nitrogen species to quaternary nitrogen by heat treatment above 900 °C. • Selective adsorption of nitrate onto N-Q site from contaminated water. • Possible inhibition of nitrate adsorption by carbonyl (C = O) and/or pyridinic nitrogen (N-6) on Cπ graphene sites. Quaternary nitrogen (N-Q) functionalized porous carbon could be prepared from thermally stabilized polyacrylonitrile (PAN) fiber (PYR) by ZnCl 2 activation (PYR-7Z4) and consecutive heat treatment at 950 °C (PYR-7Z4-9.5HT10). The prepared carbonaceous adsorbents could effectively remove nitrate anion from water by 0.6 mmol/g or more in the wide range of equilibrium solution pH (pH e) 3–8. Although the adsorption amounts on the materials derived from PYR were about a half of ion-exchange resin (HP555), fairly good adsorption performance could be realized as carbonaceous materials compared with the other carbon based adsorbents containing nitrogen species. This is caused by the presence of the equivalent N-Q sites on the prepared porous PAN carbon surface. Examining adsorption isotherms of nitrate, PYR-7Z4-9.5HT10 exhibited a little better performance than PYR-7Z4. Comparing adsorption performance of nitrogen-doped rayon based activated carbon fiber (ACF) prepared in our previous study, N-Q sites could be dominantly introduced on carbon surface for the materials derived from PYR. In addition, post heat treatment at 950 °C also seems to be effective to reduce unexpected negatively charged carboxy groups leading to the increase in both adsorption capacity and affinity of nitrate on the carbon surface. [ABSTRACT FROM AUTHOR]

Toxicity characteristic leaching procedure (TCLP) leached biochar is studied for adsorption of methylene blue (MB). Rice straw biochar obtained from slow pyrolysis at 400, 500, and 600 °C, respectively, is TCLP leached to furnish leached biochar, BL4, BL5, and BL6. The leached biochar BL4–6 have been characterized for pH, CHN analysis, ash, zeta potential, surface area morphology and functional groups. Batch adsorption studies are optimized for pH (3–9), adsorbent dose (0.5–4 g L−1), and initial MB concentration (20–135 mg L−1). Nonlinear fitting to Langmuir, Freundlich, and Redlich‐Peterson adsorption isotherm with due statistical treatment and error function analysis is carried out. Leached biochar, BL4, BL5, and BL6, is characterized by the dominance of carboxylic acid, lactone, and phenols moieties, respectively. The MB adsorption on leached biochar exhibits maximum adsorption of 26.87, 51.34, and 18.83 mg g−1 for BL4, BL5, and BL6, respectively. The underlying mechanism for adsorption of MB using BL5, is characterized by non‐ionic lactone ring opening in presence of MB under alkaline conditions that is supported by X‐ray photoelectron spectroscopy(XPS) and Fourier transformed infrared spectroscopy (FTIR) studies. Desorption of MB and regeneration from BL5 is studied with methanol and 0.1 m HCl as stripping solvent for four cycles. Recovery of MB is better with methanol in comparison to 0.1 m HCl. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization (HTC) is a thermochemical process, where biomass is treated in the presence of water at subcritical condition to produce functionalized carbon-rich solid materials known as hydrochar. Hydrochar has a core and shell structure which contains both acidic and basic functional groups but has very small surface area. Pyrolysis is often performed to expose pores and corresponding functional groups of amorphous carbon materials like hydrochar. The aim of this work was to quantify the basic functional groups on hydrochars and the effect of pyrolysis temperature on these basic functional groups. Hydrochars were produced from cellulose and wood at 220 and 260 °C followed by pyrolysis on the corresponding hydrochars at 400, 500, and 600 °C under N2 environment. Afterward, FTIR and Boehm titration (direct method) were performed to identify and quantify the basic functional groups, respectively. HTC treatment reduced the basic groups on the cellulose from 89.3 ± 3.0 to 13.6 ± 6.0 μmol/g and the wood surface from 160.0 ± 10.0 to 64.7 ± 6.5 μmol/g mainly due to the dehydration reaction and formation of a condensation layer. Pyrolysis resulted in a continuous increase of basic groups on cellulose hydrochar produced at 220 °C, while a significant increase from 13.6 ± 6.0 to 55.3 ± 9.8 μmol/g was observed during low temperature pyrolysis and remains similar at high temperature for cellulose hydrochar produced at 260 °C. In contrast, the basic functional groups increased from 59.6 ± 10.8 to 214.9 ± 8.8 μmol/g and from 64.7 ± 6.5 to 154.0 ± 8.5 μmol/g with pyrolysis temperature of wood hydrochars produced at 220 and 260 °C, respectively. The significant difference between wood and cellulose-derived pyrolyzed hydrochars could be due to the presence of lignin in wood. [ABSTRACT FROM AUTHOR]

Gasification converts coal into syngas (CO and H 2) for downstream utilization. The most important reaction in an autothermal gasifier is the char−H 2 O/CO 2 reaction. The evolution of C(O) complexes on the coal char surface directly determines the pathways and rates of CO and H 2 generation. This study mainly used a fixed bed reactor to prepare Zhundong coal char with different reaction levels in H 2 O and CO 2 , and its surface carboxyl, lactone, phenolic hydroxyl, and hydroxyl functional groups were systematically analyzed by using Boehm titration, FT-IR, and XPS. The results show that the contents of the four oxygen-containing groups in raw coal are in the order of carboxyl＞lactone＞phenol hydroxyl＞hydroxyl. In H 2 O gasification, the lactone groups were more susceptible to H 2 O resulting in a significant increase in carboxyl content at the early stage of the reaction. The hydroxyl, as a very active group in the reaction, and the amount of its generation and consumption was very obvious. The phenolic hydroxyl−the least thermally stable group among these four types of groups, was unable to participate in the inter-transformation between oxygen-containing functional groups during the gasification. During CO 2 gasification, the hydroxyl was rapidly consumed at the initial stage of the reaction and then shown a slow growth trend, and the newly generated hydroxyl would continue to undergo dehydrogenation to form new functional groups. At the end of the reaction, the transformation of other oxygen-containing functional groups into more stable carbonyl groups leads to a sudden increase in the content of carboxyl and lactone. In this work, Boehm titration was introduced into the determination of oxygen-containing functional groups on the surface of char during gasification in H 2 O/CO 2. • Evolution of oxygen-containing functional groups on coal char surface during gasification was revealed. • The evolution of oxygen-containing groups in H 2 O/CO 2 was significantly different. • H 2 O has more noticeable effect in increasing aromatic C=C of char than CO 2 during gasification. [ABSTRACT FROM AUTHOR]

Critical point (CP) in a titration curve to quantify carboxylic, lactonic, and phenolic groups on multi-walled carbon nanotube (CNT) and Vulcan carbon (VC). Titration technique used was Boehm type and tipping point measurement from titration curve was done by second derivative method. The calculation functional groups on nanocarbons (NCs) presents lowest uncertainty previously published. An order of ± 1 0 − 4 meq/g is the precision of the values obtained, one order of magnitude below reported. Both NCs display a high quantity of carboxylic groups created after being treated with regard to the other functional groups generated, mainly for functionalized Vulcan carbon VC-F. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlight • This work presents a novel Novel Flexible Ag nanoparticles doped on Graphene – Ba 2 GaInO 6 (G-BGI@Ag) for DSSCs. • This material has high conversion efficiency above 9.90%. • The different atomic percentages of Ag (2–6 wt%) on G-BGI@Ag were studied. • The functional groups of G-BGI@Ag were also studied by use of the Boehm titration method. Abstract In this study, we have demonstrated the first report on Ag nanoparticles doped on Graphene - Ba 2 GaInO 6 (G-BGI@Ag), which was synthesized by a simple hydrothermal process for improving the counter electrode (CE) in dye-sensitized solar cells (DSSCs). Ag noble metallic nanoparticles can improve chemical and electronic properties by the localized surface Plasmon resonance effect. Therefore, the different atomic percentages of Ag (2–6 wt%) on G-BGI@Ag were studied. The 6% G-BGI@Ag showed an excellent power conversion efficiency (PCE) at 9.90%, which was similar to the Pt CE under the same conditions. The functional groups of G-BGI@Ag were also studied by use of the Boehm titration method. This was because of its enhancement to the adsorption properties and reactivity levels. Moreover, the positive synergistic effect between the BGI@Ag and graphene of the composite exhibited multifunctional characteristics of high photo activity, which could serve as a guideline in photovoltaic high-efficiency multifunctional devices. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • GAC was used as metal-free catalyst to activate PS. • A remarkable synergistic effect was observed in the GAC/PS combined system. • PS concentration is more effective than GAC dosage on the MTZ removal. • The oxidation of MTZ occurred on the surface or in the boundary layer around GAC. Abstract In this work, activation of persulfate (PS) and hydrogen peroxide (H 2 O 2) in the presence of granular activated carbon (GAC) was studied in order to investigate the degradation of Metronidazole (MTZ) antibiotic in aqueous solution. The results showed that GAC could activate PS effectively better than H 2 O 2. Also, both adsorption and oxidation process induced MTZ removal in the GAC/PS system with remarkable synergistic effect in the combined system. After 240 min, 50% of PS was degraded and 80% of MTZ and 65% of COD were removed under the ambient conditions containing initial MTZ concentration of 100 mg L−1, PS/MTZ molar ratio of 100/1, GAC dosage of 5 g L−1 and initial pH of 3.9. Both PS degradation and MTZ removal followed pseudo first order kinetic with rate constant of 0.0006 min−1 and 0.0023 min−1, respectively. Scavenging study using methanol and phenol as a radical scavenger showed that most oxidation of MTZ occurred on the surface or in the boundary layer around catalyst. It was also found that MTZ removal efficiency increased when PS concentration or GAC dosage increased. However, results showed that PS loading is more effective than GAC dosage. The MTZ removal efficiency was still considerable after 4 runs reusability of GAC which implied in-situ regeneration of catalyst. It can be concluded that GAC is a favorable and promising metal-free catalyst for wastewater treatment utilization. [ABSTRACT FROM AUTHOR]

Highlights • HTC converts biomass into acidic hydrochars. • Hydrochars get closer to the neutral charge with the rise of HTC temperature. • Acidic functional group increases with the HTC temperature. Abstract The aims of this work were to quantify chemical states associated with the pH, dissociation constants, and pH at point of zero charge (pH PZC) of hydrochar and to quantify the acidic functional groups on hydrochar surface. Hydrochars from cellulose and wood treated at 180, 220, and 260 °C with 30 min residence time were produced. Boehm titration was applied to analyze acidic functional groups and dissociation constants on hydrochar surfaces. FTIR spectroscopy was used to identify the functional groups qualitatively. The results of this study indicate that hydrochar becomes more acidic due to a larger number of acidic functional groups on the hydrochar surface with the increase of hydrothermal carbonization (HTC) temperature. The total number of acidic functional groups increased from 20.5 ± 0.3 μmol/g to 1267.9 ± 22.5 μmol/g and 576.6 ± 7.8 μmol/g to 680.8 ± 18.8 μmol/g for cellulose and wood, respectively. [ABSTRACT FROM AUTHOR]

Removal of methyl iodide (CH 3 I) from the air present within nuclear facilities is a critical issue. In case of any nuclear accident, there is a great need to mitigate the radioactive organic iodide immediately as it accumulates in human bodies, causing severe consequences. Current research focuses on removing organic iodides, for which the surface of activated carbon (AC) was modified by impregnating it with different metals individually, i.e. Ag, Ni, Zn, Cu and with the novel combination of these four metals (AZNC). After the impregnation of metals, triethylenediamine (TEDA) was coated on metal impregnated activated carbon (IAC) surface. The adsorption capacity of the combination of four metals IAC was found to be 276 mg/g as the maximum for the trapping of CH 3 I. Whereas TEDA-metal impregnation on ACs enhanced the removal efficiency of CH 3 I up to 352 mg/g. After impregnation, adsorption capacity of AZNC and AZNCT is significantly higher as compared to AC. According to the finding, t 5% of AZNCT IAC is 46 min, which is considerably higher than the t 5% of other tested adsorbents. According to isotherm fitting data, Langmuir isotherm was found superior for describing CH 3 I sorption onto AC and IACs. Kinetics study shows that pseudo second order model represented the sorption of CH 3 I more accurately than the pseudo first order. Thermodynamic studies gave negative value of ΔG which shows that the reaction is spontaneous in nature. Based on the findings, AZNCT IAC appears to have a great potential for air purification applications in order to obtain clean environment. • Metals and tertiary amine impregnated activated carbons were synthesized, for the removal of methyl iodide • AC and impregnated ACs samples characterized by XRD, SEM, EDX, BET, TGA and AAS • Enhanced efficiency of AZNCT impregnated AC for removal of CH 3 I up to 352 mg/g under severe conditions • Metal-TEDA impregnated ACs considered to be promising agent for the removal of radioactive CH 3 I in the context of nuclear power plant [ABSTRACT FROM AUTHOR]

With the increasing needs of clean water supplies, the use of biomass wastes and residues for environmental remediation is essential for environmental sustainability. In this study, the residues from winery and citrus juice industries, namely grape skin and orange peel, respectively, were first converted to hydrochars by hydrothermal carbonization (HTC) and then a cationic dye (methylene blue) adsorption was studied on hydrochars. Hydrochars from both feedstocks were produced at three different temperatures (180, 220, and 250 °C) and a fixed residence time (1 h) to evaluate the hydrochar’s performance on the dye adsorption. The hydrochars were characterized in terms of their pH, pH at point of zero charge (pHPZC), surface functionalities, and surface area. A batch adsorption study of the dye was carried out with variable adsorbate concentration, pH, and temperature. Two adsorption isotherms namely Langmuir and Freundlich models were fitted at 4, 20, and 36 °C. The thermodynamic properties of adsorption (Gibbs free energy (ΔG), enthalpy (ΔH) and entropy (ΔS)) were evaluated from the isotherms fittings. Results showed that the dye adsorption on both hydrochars was significant and followed Langmuir isotherm. The maximum adsorption capacity on citrus waste hydrochar was higher than the winery waste hydrochar at any corresponding HTC temperature. Although hydrochars showed the lowest surface area (46.16 ± 0.11 and 34.08 ± 1.23 m2/g for citrus and winery wastes, respectively) at 180 °C, their adsorption was the highest, owing to their maximum density of total oxygen functional groups (23.24 ± 0.22 and 32.69 ± 1.39 µmol/m2 for citrus and winery wastes, respectively), which decreased with the increase in HTC temperature. This research shows a sustainable route for the production of highly effective adsorbent materials at lower HTC temperatures from citrus and winery wastes.

The paper introducedeffects of modified pyrolysis tar on flue gas desulfurization. This experiment selected the pyrolysis tar as the raw material, researched the effects on desulfurization performance under different modification solution, concentration, solid liquid ratio of pyrolysis tar and modified solution, calcination temperature and calcination time by 16 group orthogonal experiments. The results showed that: (1) The significance of five factors impact on the modified pyrolysis tar desulfurization performance in order was: types of the modified solution > modification solution concentration > calcination time > solid-liquid ratio > calcination temperature. (2) The modified effects of nitric acid and phosphoric acid were better. (3) The higher nitrate concentration, the better modified effect of pyrolysis tar. (4) The rate of desulfurization increased mainly associated with acidic groups on the surface of the pyrolysis tar, desulfurization performance get better along with the acidic groups increasing.

Nature of carbon nanotubes (CNTs) varies depending on extend of nanotubes surface oxidation. Chemical oxidation is one of the most widely applied methods in altering the undesired properties of CNTs such as chemical inertness and seamless surface nature. In this research, various oxidizing agents include HNO3, H2SO4, HNO3/H2SO4 and KMnO4 were investigated to assess their effectiveness on covalent functionalization of multiwalled CNTs (MWCNTs). The effects of different oxidizing agent on incorporation of functional groups and development of new defects on nanotubes sidewall are closely associated with their oxidation behavior. FTIR, Boehm titration method, XPS, Raman spectroscopy, and TEM were performed to examine the surface chemistry, extend of oxidation, and surface morphology of MWCNTs. The results revealed that HNO3/H2SO4 mixture is most effective oxidant in incorporating functionality groups on nanotubes surface, as indicated by highest functional groups concentration of 1.625 mmol/gCNTs. The completeness of nanotubes structure was successfully preserved under aggressive treatment, although some defective cylindrical graphene sheets and surface erosion were appeared under the visualization of TEM. [ABSTRACT FROM AUTHOR]

The adsorption mechanism of pertechnetate on activated carbon (AC) has been studied. For this work, the surface of commercial AC was modified using various oxidizing and reducing agents. The changes of surface functional groups were monitored by FT-IR spectroscopy and Boehm titration. The distribution coefficient (Kd) of TcO4− on the modified AC has been determined. In acidic media, the value of Kd slightly increased owing to the reductive treatment of ACs, whereas a large decrease in Kd was observed in case of oxidative treatment of ACs. Based on this work, the previous adsorption mechanisms for TcO4− on AC were examined. As an alternative adsorption mechanism, the adsorption by electrostatic attraction between TcO4− and protonated basic sites on AC surface was proposed. [ABSTRACT FROM AUTHOR]

In this work, surface-functionalization agents and various salts as auxiliaries were used to improve the adsorption capacity of biochars produced via hydrothermal carbonization of glucose, cellulose, and hazelnut shell. The effect of surface functionalization with different acids and bases as well as neutral salts on the adsorption of methylene blue and methyl orange was investigated using Boehm titration, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy techniques. Surface functionalization of biochars leads to an increase in the number of oxygen-containing functional groups on the surface, thus increasing the adsorption capacity. To probe the influence of ionic strength on the adsorption process, three auxiliaries, namely potassium chloride, cetyltrimethylammonium bromide, and sodium bicarbonate, were examined. The increase in total electrolyte concentration significantly affected the pH of the solution and as a result electrostatic interactions between dyes and biochars. Dye adsorption capacities reached 234.57 mg/g for methylene blue and 306.13 mg/g for methyl orange in the presence of cellulose-based and NaOH-functionalized biochar and glucose-based H2SO4-functionalized biochar, respectively. [ABSTRACT FROM AUTHOR]

The objective of this paper was the investigation of steam activation and mild air oxidation of biochar produced by using the Pyrovac Inc. vacuum pyrolysis for a biomass feedstock composed of a 20% volume fraction of (spruce and fir) with pine (stem of Pinus strobus without bark), with a moisture mass fraction of 10%. The biochar was activated at 900 °C under a steam partial pressure of 53 kPa over 60 min. The steam activated sample was then submitted to a mild oxidation process through a reactor fed with 164 cm 3 min −1 of air at 200 °C under 100 kPa total pressure for 60 min. Biochar was also submitted to this mild oxidation process under the same conditions except for the oxidation time which was either 30 or 60 min. The samples were analyzed using techniques including proximate and elemental analysis, Brunauer-Emmett-Teller (BET) analysis for surface area and pore size distribution by non-local density functional theory (NLDFT), scanning and transmission electron microscopy (SEM/EDX and TEM), Boehm titration, Fourier transform infrared spectroscopy (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS). The BET surface area was increased from 50 to 1025 m 2 g −1 upon steam activation while the concentration of functional groups was extensively decreased. Upon mild air oxidation, the concentration of functional groups in biochar was increased from 44 to 104.6 μmol m −2 in oxidized biochar. Combined elemental analysis and XPS results indicated that mild air oxidation generated a more uniform spatial distribution of oxygenated functional groups than in the biochar. [ABSTRACT FROM AUTHOR]

Radioactive iodine may be released into off-gas streams during both, the normal operation and severe accident of nuclear power plant in both organic and inorganic forms. Methyl iodide formation results from the reaction between radioactive iodine and organic products (like paint and cable coatings) present within the containment. For the removal of methyl iodide (MeI) gas, activated carbon (AC) was impregnated with 2, 5, 8 and 10 wt% of hexamethylenetetramine (HMTA) and triethylenediamine (TEDA). Characterization of the raw and impregnated activated carbon (IAC) was done by XRD, SEM, Raman, BET and TGA. Removal efficiency of MeI was evaluated using breakthrough experiments by varying weight percent of TEDA and HMTA. Both TEDA and HMTA-rich AC exhibited significant MeI adsorption capacity. TEDA-IAC was more effective for the elimination of MeI which adsorbed maximum 473 mg/g at low temperatures, whereas HMTA-IAC with high porosity had a comparatively high adsorption capacity at high temperatures due to its stability as compared to TEDA-IAC and adsorbed maximum 245 mg/g MeI. When raw AC was compared to IACs, results demonstrated that adsorption capacity of MeI improved up to 64 % for TEDA and 54 % for HMTA impregnated ACs. Langmuir model was well fitted to adsorption equilibrium data, and second-order model explained adsorption kinetics. Thermodynamic parameters study confirmed that the reaction is exothermic and spontaneous in nature. [Display omitted] [ABSTRACT FROM AUTHOR]

Practical aspects of the Boehm titration method are evaluated for obtaining reliable results in the quantification of oxygen-containing surface groups in a short time. Analytical criteria such as accuracy, repeatability, precision, and robustness are applied. Oxidized multi-walled carbon nanotubes (MWCNTs) are used as the model substance. Different reaction bases (NaHCO3(aq), Na2CO3(aq), NaOH(aq)) are applied and treatment times are studied. We also show that smaller amounts of carbon material can be reliably analyzed by using an autotitrator combined with a pH electrode. We find that indirect titration with Na2CO3 results in the highest titration precision and accuracy despite the lower base strength compared with NaOH. Therefore, CO2 impurities do not have to be removed and only 7 min is necessary for one titration. The titration error with respect to the proposed method is 0.15% of the aliquot volume. The mixing method during the carbon treatment with bases (stirring, shaking, ultrasound treatment) has no influence on the result as long as one allows a few hours for the reaction to complete. Finally, we provide a standard operating procedure for obtaining results with high precision during Boehm titration.

The use of the Boehm titration (BT) method as an analytical tool for the quantification of oxygen-containing surface groups is systematically investigated for oxidized carbon black, carbon nanotubes and two active carbons with specific surface areas between 60 and 1750 m2 g−1. The accuracy of the BT method is quantitatively compared with results from elemental analysis (EA), temperature programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). Overall, the results from TPD are in line with the values obtained by BT. Both show the equal ratio of the oxygen groups to each other. Within the series of carbon samples, all methods provide similar trends for the total oxygen content yet the absolute numbers are deviating significantly. Reasons for these discrepancies are discussed and linked to the specific characteristics of the different methods. As the BT method is a solution based method, it only probes the surface fraction of the carbon that is accessible to the base solution. That means, it probes the relevant fraction for applications where carbon is in contact to aqueous solutions. Overall, the BT method can be conveniently applied to a broad range of carbon materials as long as the samples are sufficiently hydrophilic and of the enough sample amount is provided.

Hydrochar has been gaining tremendous interest as adsorbent materials, however, change in material properties due to process liquid recirculation needs to be explored, since commercial hydrothermal carbonization (HTC) is likely to recycle HTC process liquid in order to preheat the feedstock as well as minimize the wastewater accumulation. Therefore, this study focused on the process liquid recirculation up to 9 times and evaluated how surface functionalities as well as Rhodamine B adsorption capacities change with the number of recycle. HTC of corn stover was performed at a fixed temperature (230 °C) and a fixed residence time (30 mins) with 50 wt% process liquid recirculation. Results indicate that the mass yield for control was 60.6 ± 0.9 wt% which was increased to 66.9 ± 0.0 wt% with HTC process liquid recirculation. Meanwhile, ash was concentrating with HTC process liquid recirculation (from 10.3 ± 1.1% to 13.9 ± 0.3%). The Brunauer, Emmett, and Teller (BET) surface area and total pore volume for control were 6.7 ± 0.1 m2/g and 9.8 × 10−3 cm3/g, respectively, which were increased to 7.4 ± 0.0 m2/g (recycle-1) - 10.8 ± 0.1 m2/g (recycle-9) and 12.4 × 10−3 cm3/g (recycle-1) − 17.3 × 10−3 cm3/g (recycle-9). However, Boehm titration revealed that the recycle-3 retained higher oxygen-containing surface functional group density (231.2 ± 3.9 µmol/g) than control (161.9 ± 2.5 µmol/g) and recycle-9 (132.2 ± 1.5 µmol/g). These morphological characteristics also reflect on the Rhodamine B adsorption capacities, where maximum equilibrium adsorption capacity was found for recycle-3 (30.7 mg/g) followed by recycle-9 (23.6 mg/g) and control (21.4 mg/g) and the adsorption isotherms were following combined Langmuir-Freundlich isotherm. [Display omitted] • Solid mass yield was increased for recycle-1 and reached equilibrium. • CHNO and ash retainment efficiency was increased upto recycle-3 and 7, respectively. • Max. equilibrium adsorption capacity for Rhodamine B was increased upto recycle-3. • Best fitted adsorption isotherm model was combined Langmuir-Freundlich isotherm. [ABSTRACT FROM AUTHOR]

The study focused on the adsorption mechanism of two selected pesticides: carboxin and diuron, on goethite and biochar, which were treated as potential compounds of mixed adsorbent. The authors also prepared a simple mixture of goethite and biochar and performed adsorption measurements on this material. The adsorbents were characterized by several methods, inter alia, nitrogen adsorption/desorption, Boehm titration, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The adsorption study included kinetics and equilibrium measurements, in the solution containing one or two pesticides simultaneously. The adsorption data were fitted to selected theoretical models (e.g., Langmuir, Freudlich, Redlich–Peterson, pseudo first-order and pseudo second-order equations). Based on the obtained results, it was stated that, among all tested adsorbents, biochar had the highest adsorption capacity relative to both carboxin and diuron. It equaled 0.64 and 0.52 mg/g, respectively. Experimental data were best fitted to the pseudo second-order and Redlich–Peterson models. In the mixed systems, the adsorption levels observed on biochar, goethite and their mixture were higher for diuron and lower for carboxin, compared to those noted in the single solutions. The presented results may enable the development of new mixed adsorbent for remediation of soils polluted with pesticides. [ABSTRACT FROM AUTHOR]

• Hydrophobicity of the hydrochar increased with the increase of hydrothermal treatment (HTT) temperature. • Maximum oxygen-containing acidic functional groups of cellulose hydrochar were experienced at 260 °C. • Particle size of hydrochar increased with the HTT temperature and finally collapsed at the highest temperature. • Hydrochars showed both amorphous and crystalline structures under HTT condition. Hydrochar, used for numerous applications including solid fuel, adsorbent medium, anode material, and soil amendment, is the major solid product or unwanted byproduct resulting when biomass undergoes for subcritical or supercritical water treatment, respectively. Regardless of the reaction temperature, hydrochar forms from biomasses at different reaction kinetics. Our hypothesis in this study is morphology and oxygen functionality of hydrochar change with reaction temperature, especially from a subcritical to supercritical region. To test this hypothesis, hydrochar was produced from microcrystalline cellulose at 220 °C–420 °C with 40 °C interval with a reaction time of 30 min. The effects of subcritical and supercritical conditions of the hydrochar characteristics were investigated using a series of analytical tools including ultimate and proximate analyses, Brunauer-Emmett-Teller (BET) surface area, scanning electron microscopy (SEM), X-Ray Diffraction (XRD) analysis, Fourier-transform infrared spectroscopy (FTIR), and Boehm Titration. Results showed that oxygen-containing acidic functional groups reached the highest (1495 ± 25 μmol/g) at 260 °C and reduced afterward with an increase of temperature, although the elemental oxygen was reduced with the increase of reaction temperature. The particle size of hydrochar increases with the increase of temperature in the subcritical region but decreases in the supercritical region. [ABSTRACT FROM AUTHOR]

With the increasing needs of clean water supplies, the use of biomass wastes and residues for environmental remediation is essential for environmental sustainability. In this study, the residues from winery and citrus juice industries, namely grape skin and orange peel, respectively, were first converted to hydrochars by hydrothermal carbonization (HTC) and then a cationic dye (methylene blue) adsorption was studied on hydrochars. Hydrochars from both feedstocks were produced at three different temperatures (180, 220, and 250 °C) and a fixed residence time (1 h) to evaluate the hydrochar's performance on the dye adsorption. The hydrochars were characterized in terms of their pH, pH at point of zero charge (pHPZC), surface functionalities, and surface area. A batch adsorption study of the dye was carried out with variable adsorbate concentration, pH, and temperature. Two adsorption isotherms namely Langmuir and Freundlich models were fitted at 4, 20, and 36 °C. The thermodynamic properties of adsorption (Gibbs free energy (ΔG), enthalpy (ΔH) and entropy (ΔS)) were evaluated from the isotherms fittings. Results showed that the dye adsorption on both hydrochars was significant and followed Langmuir isotherm. The maximum adsorption capacity on citrus waste hydrochar was higher than the winery waste hydrochar at any corresponding HTC temperature. Although hydrochars showed the lowest surface area (46.16 ± 0.11 and 34.08 ± 1.23 m2/g for citrus and winery wastes, respectively) at 180 °C, their adsorption was the highest, owing to their maximum density of total oxygen functional groups (23.24 ± 0.22 and 32.69 ± 1.39 µmol/m2 for citrus and winery wastes, respectively), which decreased with the increase in HTC temperature. This research shows a sustainable route for the production of highly effective adsorbent materials at lower HTC temperatures from citrus and winery wastes. [ABSTRACT FROM AUTHOR]

Natural graphite, a locally available, eco-friendly, and low-cost carbonaceous source, can be easily transformed into exfoliated graphite (EG) with many surface functional groups via a chemical oxidation route. Combination between EG and magnetic MnFe2O4 is a promising strategy to create a hybrid kind of nanocomposite (EG@MnFe2O4) for the efficient adsorptive removal of Congo red (CR) dye from water. Here, we reported the facile synthesis and characterization of chemical bonds of EG@MnFe2O4 using several techniques such as Fourier-transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). In particular, the quantity method by Boehm titration was employed to identify the content of functional groups: Carboxylic acid (0.044 mmol/g), phenol (0.032 mmol/g), lactone (0.020 mmol/g), and total base (0.0156 mmol/g) on the surface of EG@MnFe2O4. Through the response surface methodology-optimized models, we found a clear difference in the adsorption capacity between EG-decorated MnFe2O4 (62.0 mg/g) and MnFe2O4 without EG decoration (11.1 mg/g). This result was also interpreted via a proposed mechanism to elucidate the contribution of surface functional groups of EG@MnFe2O4 to adsorption efficiency towards CR dye. [ABSTRACT FROM AUTHOR]

It is well known that surfactant-suspended carbon nanotube (CNT) samples can be purified by centrifugation to decrease agglomerates and increase individually-dispersed CNTs. However, centrifugation is not always part of protocols to prepare CNT samples used in biomedical applications. Herein, using carboxylated multi-walled CNTs (cMWCNTs) suspended in water without a surfactant, we developed a Boehm titrimetric method for the analysis of centrifuged cMWCNT suspensions and used it to show that the surface acidity of oxidized carbon materials in aqueous cMWCNT suspensions was enriched by ~40% by a single low-speed centrifugation step. This significant difference in surface acidity between un-centrifuged and centrifuged cMWCNT suspensions has not been previously appreciated and is important because the degree of surface acidity is known to affect the interactions of cMWCNTs with biological systems., Competing Interests: The authors have no conflicts of interest to declare.