Boehm Titration Revisited (Part I): Practical Aspects for Achieving a High Precision in Quantifying Oxygen-Containing Surface Groups on Carbon Materials

Assessing the Acidic and Alkaline Recalcitrance of Covalently Modified Surface Amines on Ordered Mesoporous Carbon

Ordered mesoporous carbon (OMC) scaffolds were covalently modified with primary amine groups by means of oxidation-coupling, yielding C-O-C bonds, or organometallic activation-coupling, yielding C-C bonds. The aminated OMCs were stressed by immersion in either 1 M hydrochloric acid or 1 M sodium hydroxide solutions at room temperature for 6 h and characterized by nitrogen sorption, electron microscopy, low-angle X-ray diffraction, thermogravimetric analysis, and the 4-nitrobenzaldehyde assay. Results demonstrate that aminated surfaces of OMC by butyllithium grafting are stable toward both 1 M HCl and 1 M NaOH, whereas the oxidation-aminated OMC surfaces can withstand 1 M NaOH only. This study illustrates the importance of chemical testing to supplant chemical intuition when tailoring carbon surfaces for applications where strong acids or bases are employed. This is especially emphasized for carbonaceous materials because of the surface heterogeneity among different carbon allotropes.

Adsorption dynamics of Cd2+(aq) on microwave-synthetized pristine biochar from cocoa pod husk: Green, experimental, and DFT approaches

Biochar obtained via microwave-assisted pyrolysis (MAP) at 720 W and 15 min from cocoa pod husk (CPH) is an efficient adsorbent of Cd2+(aq). Biochar of residual biomass of CPH (BCCPH) possesses favorable physicochemical and morphological properties, featuring a modest surface area yet a suitable porous structure. Adsorption, predominantly governed by physisorption, is influenced by the oxygen-containing active sites (-COOR, -C(R)O, and -CH2OR; R = H, alkyl). CdCO3 formation occurs during adsorption. Experimental data were well-fitted into various kinetic models for a broad understanding of the sorption process. Langmuir model indicates a maximum adsorption capacity of 14.694 mg/g. The thermodynamic study confirms the spontaneous and endothermic sorption. Studies at the molecular level have revealed that the Cd2+ ion tends to bind to surface aromatic carbon atoms. This sustainable approach produces BCCPH via MAP as a solution for waste transformation into water-cleaning materials.

Characterization of Magnetic Biochar Modified Using the One-Step and Electrochemical Methods and Its Impact on Phosphate Adsorption

The properties and phosphate adsorption capability of the one-step method and electrochemical method in modifying peanut shell biochar have been determined. The one-step method deposits MgO and Fe3O4 onto biochar through chemical impregnation and regularly affects the functional groups and magnetic separation of biochar, thereby enhancing its ability to adsorb phosphate. In contrast, the electrochemical method is not favorable for modifying functional groups of biochar but can promote phosphate adsorption because of the formation of MgFe2O4 and Fe3O4 using electrolysis. The adsorption isotherm and kinetics data suggest that adsorption is monolayer onto a homogeneous surface and phosphate adsorption could be controlled by chemical processes. Biochar with the addition of both Fe2+ and Mg2+ shows better phosphate adsorption capability than those with barely any Fe2+ additions. It was concluded that the one-step method is a better modification method than the electrochemical method for enhancing the phosphate adsorption capability of biochars.

Chlorphenamine adsorption on commercial activated carbons: Effect of Operating Conditions and Surface Chemistry

Chlorphenamine (CPA) adsorption onto three activated carbons (ACs), namely, Megapol M (MM), Micro 10 (M10), and GAMA B (GB), was studied in this work. The textural properties, concentrations of active sites, surface charge and point of zero charge of the ACs were assessed. The surface areas (SBET) of MM, GB and M10 were 1107, 812 and 766 m2/g, respectively. The MM surface had an acidic character, while the surfaces of M10 and GB were basic. The adsorption capacity of MM, M10, and GB towards CPA was studied at pH 7 and 11, and the adsorption capacity decreased in the order MM > M10 ≈ GB, which was ascribed to the magnitude of SBET and the concentration of acidic sites. The solution pH significantly increased the adsorption capacity of MM towards CPA by raising the solution pH from 5 to 9, and this behavior was attributed to the electrostatic attraction between the negatively charged surface of MM and the cationic species of CPA. The maximum uptake of CPA adsorbed on MM was 574.6 mg/g at pH = 11 and T = 25 °C. The adsorption capacity of MM was slightly raised by incrementing the temperature. Lastly, the zeta potential measurements of pristine MM and MM saturated with CPA confirmed that the electrostatic attraction predominated in the pH range of 5-9, and the π-π stacking interactions were the principal mechanism of CPA adsorption on MM at pH 11.

Assessment of the Porous Structure and Surface Chemistry of Activated Biocarbons Used for Methylene Blue Adsorption

In the presented research, activated carbons from wheat bran were obtained as a result of pyrolysis and physical activation (CO₂ or/and steam). In addition, the obtained materials were subjected to additional modification with superheated steam using the microwave radiation as an energy source. The detailed materials characterization was performed using low-temperature nitrogen adsorption/desorption, Raman spectroscopy, X-ray diffraction, thermal analysis (TG), Boehm's titration, point of zero charge (pH_pzc), scanning electron microscopy (SEM) and FT-IR/ATR methods. Moreover, the sorption capacity towards methylene blue (MB) was determined. The activated carbons were characterized with a well-developed surface and pore structure (S_BET = 339.6-594.0 m²/g; V_p = 0.157-0.356 cm³/g). Activation in the presence of steam and additional modification with microwave radiation resulted in much better development of the porous structure (S_BET = 600.4 m²/g; V_p = 0.380 cm³/g). The materials were shown to possess amorphous structure and thermal stability up to the temperatures of ~450-500 °C. They have good adsorption capacity towards MB varying from 150 mg/g to 241 mg/g depending on activation manner. The adsorption can be described by the pseudo-second order model (R² = 0.99) and fitted to the Langmuir isotherm.

Physical-Chemical Characterization of Different Carbon-Based Sorbents for Environmental Applications

Biochar has been used in various applications, e.g., as a soil conditioner and in remediation of contaminated water, wastewater, and gaseous emissions. In the latter application, biochar was shown to be a suitable alternative to activated carbon, providing high treatment efficiency. Since biochar is a by-product of waste pyrolysis, its use allows for compliance with circular economics. Thus, this research aims to obtain a detailed characterization of three carbonaceous materials: an activated carbon (CARBOSORB NC 1240^®) and two biochars (RE-CHAR^® and AMBIOTON^®). In particular, the objective of this work is to compare the properties of three carbonaceous materials to evaluate whether the application of the two biochars is the same as that of activated carbon. The characterization included, among others, particle size distribution, elemental analysis, pH, scanning electron microscope, pore volume, specific surface area, and ionic exchange capacity. The results showed that CARBOSORB NC 1240^® presented a higher specific surface (1126.64 m²/g) than AMBIOTON^® (256.23 m²/g) and RE-CHAR^® (280.25 m²/g). Both biochar and activated carbon belong to the category of mesoporous media, showing a pore size between 2 and 50 nm (20-500 Å). Moreover, the chemical composition analysis shows similar C, H, and N composition in the three carbonaceous materials while a higher O composition in RE-CHAR^® (9.9%) than in CARBOSORB NC 1240 ^® (2.67%) and AMBIOTON^® (1.10%). Differences in physical and chemical properties are determined by the feedstock and pyrolysis or gasification temperature. The results obtained allowed to compare the selected materials among each other and with other carbonaceous adsorbents.

Effect of Biochar Modification by Vitamin C, Hydrogen Peroxide or Silver Nanoparticles on Its Physicochemistry and Tetracycline Removal

Chemical modification of biochars can improve their adsorption capacity relative to antibiotics, posing a serious threat to the environment. Therefore, this research is aimed at the treatment of sunflower husk biochar (BC) by vitamin C, hydrogen peroxide or silver nanoparticles and the impact of this procedure on the biochar porosity, surface chemistry, and ability to remove tetracycline (TC). During the study, BC was produced by pyrolysis of sunflower husks at 650 °C. All solids were characterized using potentiometric titration, nitrogen adsorption/desorption, Fourier transform infrared spectroscopy, etc. The experimental adsorption data was described by kinetics equations: pseudo-first order, pseudo-second order, and particle internal diffusion (IPD) models as well as by isotherms of Langmuir, Langmuir-Freundlich, and Redlich-Peterson. The obtained results indicated that the biochar upgraded by vitamin C (BCV) had the highest ability to attract antibiotic molecules and, as a result, the TC adsorption on its surface was the largest. Furthermore, the TC desorption from this material was minimal. The measured TC adsorbed amounts for the modified BCs were as follows: 47.75% (7.47 mg/g) for BCV, 37.35% (8.41 mg/g)-for biochar treated by hydrogen peroxide (BCH), and 42.04% (9.55 mg/g) for biochar modified by silver nanoparticles (BCA). The lowest adsorption level was noted for non-modified biochar, i.e., 34.17% (6.83 mg/g). Based on the presented results it can be stated that the upgraded biochars had a good potential to improve the tetracycline removal from aqueous media, e.g., groundwater.

Activated Carbon Modified by Ester Hydrolysis of Ethyl Acetate for Water Vapor Adsorption Enhancement

To improve water vapor adsorption, this study employed oxalic acid–ethyl acetate acidic hydrolysis to modify honeycomb activated carbon and introduce hydrophilic functional groups. Scanning electron microscopy (SEM), Boehm titration, Fourier transform infrared spectroscopy (FT-IR), and an automatic surface area analyzer (BET) were used to characterize the microscopic morphology, surface functional groups, specific surface area, and pore size changes. The results showed that, when the concentration of oxalic acid is 0.0006 mol/cm3, the specific surface area is 179.06 m2/g. After hydrolysis with ethyl acetate, the original functional groups became more abundant, while the number of total acidic functional groups on the surface grew from 0.497 mmol/g to 1.437 mmol/g. The static water vapor adsorption experiments were conducted on modified activated carbon under constant temperature and humidity conditions. Compared with unmodified activated carbon, the activated carbon modified with 0.0006 mol/cm3 oxalic acid increased the adsorption capacity of water vapor by 15.7%. The adsorption capacity of activated carbon after being combined with 0.0006 mol/cm3 oxalic acid and ester hydrolysis modification increased by 37.1%. At the same temperature, the adsorption capacity increased with a higher relative humidity. At the same relative humidity, the adsorption capacity decreased as the temperature rose. Therefore, this modification method may provide clues for the application of enhancing the hygroscopic ability of activated carbon.

Studying the Effect of Shortening Carbon Nanotubes via Ball Milling on Cellulose Acetate Nanocomposite Membranes for Desalination Applications

Studying the effect of different sizes of multi-walled carbon nanotubes (CNTs) on mixed matrix membranes in nanofiltration applications has not been widely reported in the literature. In this study, two different lengths of functionalized CNTs were used to investigate such effect. First, CNTs were shortened by using high-energy ball milling at 400 RPM, with a ball-to-powder weight ratio (BPR) of 120:1. Characterization of the structure of the CNTs was carried out using TEM, XRD, SEM, BET, and Raman Spectroscopy. Second, 0.001 wt % of unmilled and milled CNTs were incorporated into cellulose acetate nanocomposite membranes, Eli-0 (unmilled), and Eli-400 (milled at 400 RPM) to study their effects on the membranes’ morphology, porosity, hydrophilicity, and performance analysis in terms of permeation and salt retention rates of 5000 ppm Na₂SO₄. Results showed that shortening CNTs enhanced the membranes’ hydrophilicity and affected macrovoid and micropore formation. Furthermore, shortening CNTs resulted in opening their caps and improved the permeation rates with a slight adverse effect on salt retention.

Hydrothermal carbonization of household wet waste - characterization of hydrochar and process wastewater stream

In the present study, household wet waste (HWW) pretreatment was explored using hydrothermal carbonization (HTC) to enhance resource recovery opportunities. The pretreatment was performed at 200 °C for 1-8 h duration in a 2 L high pressure reactor. After HTC, the recovered solid hydrochar (HC) showed high calorific value of ∼ 27 MJ/kg compared to 18 MJ/kg of HWW. Moreover, it contained significant amount of oxygen containing acidic functional groups, hence the waste derived HC may also be utilized as adsorbent in wastewater treatment and soil conditioner. The process wastewater (PW) contained several value-added organics including proteins and furfurals. The HTC reaction kinetics showed the conversion of HWW to primary HC as the fastest step (rate constant = 0.0126 min^-1). Moreover, the biochemical methane potential test on PW revealed generation of significant amounts of biogas with 55-75% methane. The total energy production from HC and PW was estimated as ∼ 3.3 MJ/kg of HWW.

Determination of lead ions in fish and oyster samples using a nano-adsorbent of functionalized magnetic graphene oxide nanosheets-humic acid and the flame atomic absorption technique

This study aims at the functionalization of magnetic graphene oxide nanosheets and the binding of humic acid as a lead complex ligand. Graphene oxide nanosheets possess a large surface area and various carboxylic acid groups which can be activated easily by activating agents. Therefore, they are suitable to be used for the extraction of heavy metals. To have a better process of extracting lead ions, magnetic graphene oxide was used in this research. Humic acid, as a lead metal complex agent, has an amine functional group which can be bound to modified graphene oxide from one side. The process of constructing the nano-adsorbent proposed for the preconcentration of lead ions as well as its characterization was studied by infrared spectroscopy (IR), ultraviolet-visible spectroscopy (UV-visible), field emission scanning electron microscopy (FESEM), and vibrating sample magnetometry (VSM). The designed nano-adsorbent was tested to measure lead ions in simulated and real samples of sea water, fish, and oysters. The detection limit obtained in the simulated samples was 0.07 μg/L, and the linear range was 0.2-12 μg/L. The apparatus used to measure the ions was a flame atomic absorption device. In the analysis of the real samples, the values obtained through flame atomic absorption were compared with those obtained through furnace atomic absorption. The proposed technique is advantageous due to being cheap, precise, and sensitive for the trace measurement of lead ions.

Mechanistic insights into acetaminophen removal on cashew nut shell biomass-derived activated carbons

Activated carbons prepared from cashew nut shells by chemical activation with phosphoric acid were tested for the removal of acetaminophen. It was found that an increase in carbonization temperature resulted in increased pore volume and decreased amount of surface functional groups. Potentiometric titration analysis indicated that the majority of surface groups on carbons are acidic. Detailed surface characterization by FT-IR, XPS, and thermal analyses indicated the involvement of surface functional groups in the removal of acetaminophen either via hydrogen bonding or by acid hydrolysis. The carbon obtained at 600 °C, which contains high amount of carboxylic groups and high pore volume, exhibited the highest adsorption capacity. For this carbon, the removal of acetaminophen took place mostly via acid hydrolysis with the formation of p-aminophenol and acetic acid adsorbed on the surface. Carbon obtained at 400 °C was found to have the highest density of acidic functional groups, which resulted in dimerization reactions and pore blockage. No direct correlation was observed between the adsorption capacities of carbons and their textural or surface characteristics. This suggests the complexity of acetaminophen removal by the cashew nut shell-derived activated carbons, governed by their surface chemistry and supported by high surface area accessible via micro/mesopores.

Novel Correlations between Spectroscopic and Morphological Properties of Activated Carbons from Waste Coffee Grounds

Massive quantities of spent coffee grounds (SCGs) are generated by users around the world. Different processes have been proposed for SCG valorization, including pyrolytic processes to achieve carbonaceous materials. Here, we report the preparation of activated carbons through pyrolytic processes carried out under different experimental conditions and in the presence of various porosity activators. Textural and chemical characterization of the obtained carbons have been achieved through Brunauer–Emmett–Teller (BET), ESEM, 13C solid state NMR, XPS, XRD, thermogravimetric and spectroscopic determinations. The aim of the paper is to relate these data to the preparation method, evaluating the correlation between the spectroscopic data and the physical and textural properties, also in comparison with the corresponding data obtained for three commercial activated carbons used in industrial adsorption processes. Some correlations have been observed between the Raman and XPS data.

Activated biochar derived from spent Auricularia auricula substrate for the efficient adsorption of cationic azo dyes from single and binary adsorptive systems

In this study, spent Auricularia auricula substrate (AS)-derived biochar (ASBCs) and activated biochar with NaOH (A-ASBC) were evaluated for the adsorption of cationic azo dyes, including methylene blue (MB), rhodamine B (RB), and crystal violet (CV), from single and binary adsorptive systems. A-ASBC showed a higher maximum adsorption capacity for these dyes (MB: 53.62 mg·g^-1, RB: 32.33 mg·g^-1, CV: 735.73 mg·g^-1) than ASBCs in a single system because it had a greater specific surface area and more oxygen containing-functional groups on the surface. The adsorption process of the three dyes onto the adsorbents was in good agreement with the Freundlich adsorption isotherm and fit the pseudo-second-order kinetic model, which revealed sorbate polymolecular layer formation over the adsorbent surface and the involvement of chemisorption. The adsorption mechanism showed that the adsorption of three dyes on adsorbents could be postulated as a multistep process with extraordinary affinity-induced adsorption in terms of both physisorption and chemisorption. In the binary adsorptive system, the results showed that all MB, RB, and CV had antagonistic/competitive effects on each other's adsorption (Q_Binary/Q_Single < 1). Furthermore, a phytotoxic assay affirmed the effectiveness of the adsorbent in adsorbing dye species from aqueous solutions using Brassica pekinensis L. seeds as the model. Therefore, activated biochar prepared from AS can be used as a potentially economical and effective adsorbent for treating printing and dyeing wastewater.

Carboxin and Diuron Adsorption Mechanism on Sunflower Husks Biochar and Goethite in the Single/Mixed Pesticide Solutions

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.

Surface Modification Effect and Electrochemical Performance of LiOH-High Surface Activated Carbon as a Cathode Material in EDLC

This study aimed to improve the performance of the activated carbon-based cathode by increasing the Li content and to analyze the effect of the combination of carbon and oxidizing agent. The crystal structure and chemical structure phase of Li-high surface area activated carbon material (Li-HSAC) was analyzed by X-ray diffraction (XRD) and Raman spectroscopy, the surface state and quantitative element by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) and the surface properties with pore-size distribution by Brunauer–Emmett–Teller (BET), Barrett–Joyner–Halenda (BJH) and t-plot methods. The specific surface area of the Li-YP80F is 1063.2 m²/g, micropore volume value is 0.511 cm³/g and mesopore volume is 0.143 cm³/g, and these all values are higher than other LiOH-treated carbon. The surface functional group was analyzed by a Boehm titration, and the higher number of acidic groups compared to the target facilitated the improved electrolyte permeability, reduced the interface resistance and increased the electrochemical properties of the cathode. The oxidizing agent of LiOH treated high surface area of activated carbon was used for the cathode material for EDLC (electric double layer capacitor) to determine its electrochemical properties and the as-prepared electrode retained excellent performance after 10 cycles and 100 cycles. The anodic and cathodic peak current value and peak segregation of Li-YP80F were better than those of the other two samples, due to the micropore-size and physical properties of the sample. The oxidation peak current value appeared at 0.0055 mA/cm² current density and the reduction peak value at –0.0014 mA/cm², when the Li-YP80F sample used to the Cu-foil surface. The redox peaks appeared at 0.0025 mA/cm² and –0.0009 mA/cm², in the case of using a Nickel foil, after 10 cycling test. The electrochemical stability of cathode materials was tested by 100 recycling tests. After 100 recycling tests, peak current drop decreased the peak profile became stable. The LiOH-treated high surface area of activated carbon had synergistically upgraded electrochemical activity and superior cycling stability that were demonstrated in EDLC.

The critical contribution of oxidation debris on the acidic properties of graphene oxide in an aqueous solution

The contribution of oxidation debris (OD) to the acidity of graphene oxide (GO) was investigated in this study. With Na₂CO₃ as the titrator base, the Boehm titration results showed that the total acidity of GO in an aqueous solution decreased from 9.72 to 2.74 mmol g^-1 after a thorough removal of OD and that the total acidity of OD was 26.45 mmol g^-1. Thermogravimetric analyses showed that the mass ratios of OD and residual graphene sheets (named bwGO) were ∼26 % and ∼73 % of the whole pristine GO, respectively. Based on the quantitative relationships between the mass ratio and acid site density, it was concluded that the total acidity of GO was equal to the sum of the acidity from bwGO and the OD contained in GO. Under alkaline conditions, the splitting and stripping of OD was attributed to the combined effect of the cleavage of H-bonds by nucleophilic attack from OH- and the electrostatic repulsion due to the ionization of carboxylic acids, in which the former became dominant when the pH shifted to neutral and weakly acidic. This study provides an explanation for the origin of GO acidity in aqueous solutions and highlights the role of OD in the chemistry of GO.

Modified Activation Process for Supercapacitor Electrode Materials from African Maize Cob

In this work, African maize cobs (AMC) were used as a rich biomass precursor to synthesize carbon material through a chemical activation process for application in electrochemical energy storage devices. The carbonization and activation were carried out with concentrated Sulphuric acid at three different temperatures of 600, 700 and 800 °C, respectively. The activated carbon exhibited excellent microporous and mesoporous structure with a specific surface area that ranges between 30 and 254 m²·g^-1 as measured by BET analysis. The morphology and structure of the produced materials are analyzed through Field Emission Scanning Electron Microscopy (FESEM), Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), Boehm titration, X-ray Photoelectron Spectroscopy (XPS) and Raman Spectroscopy. X-ray photoelectron spectroscopy indicates that a considerable amount of oxygen is present in the materials. The functional groups in the activated carbon enhanced the electrochemical performance and improved the material's double-layer capacitance. The carbonized composite activated at 700 °C exhibited excellent capacitance of 456 F g^-1 at a specific current of 0.25 A g^-1 in 6 M KOH electrolyte and showed excellent stability after 10,000 cycles. Besides being a low cost, the produced materials offer good stability and electrochemical properties, making them suitable for supercapacitor applications.

Comparison of Monovalent and Divalent Ions Removal from Aqueous Solutions Using Agricultural Waste Biochars Prepared at Different Temperatures-Experimental and Model Study

Copper (Cu) and silver (Ag) occur naturally in the environment but have toxic effects on organisms at elevated concentrations. This paper discussed the removal of Cu and Ag from aqueous solutions using biochars obtained at different pyrolysis temperatures. Three biomass sources-sunflower husks (SH), a mixture of sunflower husks and rapeseed pomace (SR) and wood waste (WW)-were pyrolyzed at 300, 400 and 500 °C. Biochars produced at 500 °C exhibited a higher specific surface area, lower variable surface charge and lower contents of surface functional groups than those obtained at 400 or 300 °C. The pseudo-second-order model and intra-particle diffusion (IPD) model well-described the Cu and Ag adsorption kinetics. The Cu adsorption was about 1.48 times slower than the Ag adsorption on the biochars obtained at 500 °C. The model of Langmuir-Freundlich well-described the equilibrium adsorption. Agricultural biochars obtained at >500 °C had a surface with a higher affinity to attract Ag than Cu and were able to remove a larger amount of heavy metals from aqueous media than those prepared at lower pyrolysis temperatures.

The Proof-of-the Concept of Biochar Floating Cover Influence on Swine Manure pH: Implications for Mitigation of Gaseous Emissions From Area Sources

Mitigation of potentially hazardous and malodor compounds emitted from animal waste is needed to improve the sustainability of livestock agriculture. Bacteria control the generation of these compounds and also depend on the pH of manure. Influencing swine manure pH, especially on the liquid-air interface, may lead to a reduction of emission of odorous and hazardous compounds. The objective of this experiment was to test highly alkaline and porous (HAP) modified biochar with pH = 9.2 and red oak (RO) biochar with pH = 7.5 influence on swine manure pH acquired from the outdoor storage and deep pit storage under a barn. HAP and RO biochars were topically applied on the outdoor-stored (pH = 7.55), and pit (pH = 8.00) manures and spatial pH (every 1 mm of depth) were measured on days 0, 2, and 4. Results showed that HAP biochar increased outdoor-stored manure pH on day 4, particularly within the top 10 mm of depth, where pH ranged from 7.79 to 8.90, while in the case of RO pH ranged between 7.46 and 7.66, i.e., similar to control (7.57-7.64). Both biochars decreased pit-stored manure pH within the top 10 mm of depth (in comparison with the control pH of 8.36-8.47) to 8.19-8.30 (HAP), and 8.18-8.29 (RO) on day 4. However, differences were not considerable. The reason for the insignificant effect of biochars on pit manure was likely due to its higher buffer capacity in comparison with the outdoor-stored manure.

Conversion of Xylose to Furfural over Lignin-Based Activated Carbon-Supported Iron Catalysts

In this study, conversion of xylose to furfural was studied using lignin-based activated carbon-supported iron catalysts. First, three activated carbon supports were prepared from hydrolysis lignin with different activation methods. The supports were modified with different metal precursors and metal concentrations into five iron catalysts. The prepared catalysts were studied in furfural production from xylose using different reaction temperatures and times. The best results were achieved with a 4 wt% iron-containing catalyst, 5Fe-ACs, which produced a 57% furfural yield, 92% xylose conversion and 65% reaction selectivity at 170 °C in 3 h. The amount of Fe in 5Fe-ACs was only 3.6 µmol and using this amount of homogeneous FeCl3 as a catalyst, reduced the furfural yield, xylose conversion and selectivity. Good catalytic activity of 5Fe-ACs could be associated with iron oxide and hydroxyl groups on the catalyst surface. Based on the recycling experiments, the prepared catalyst needs some improvements to increase its stability but it is a feasible alternative to homogeneous FeCl3.

Purification of Aqueous Media by Biochars: Feedstock Type Effect on Silver Nanoparticles Removal

Due to the harmful effects of nanoparticles in the environment, their effective removal from aqueous media is of great importance. This paper described the research on the silver nanoparticles (Ag-NPs) sorption on biochars obtained from different feedstock types. The sorbents were produced through pyrolysis (double-barrel method) of the vineyard (BV), paulownia tree (BP), and tobacco (BT). BV exhibited the highest specific surface area, porosity, value of variable surface charge, and content of surface acidic functional groups among the used biochars. The pseudo-second order model best described the obtained adsorption kinetics, whereas the Freundlich model accounted for the registered adsorption data. The Ag-NPs removal was highly efficient in the case of BV, especially in the nanoparticle concentration range 50-500 mg/L. Thus, this biochar can be considered as an ecofriendly, effective, low-cost organic adsorbent, potentially used in the aqueous media purification.

Influence of Surface Modified Nanodiamonds on Dielectric and Mechanical Properties of Silicone Composites

Detonation nanodiamonds, also known as ultradispersed diamonds, possess versatile chemically active surfaces, which can be adjusted to improve their interaction with elastomers. Such improvements can result in decreased dielectric and viscous losses of the composites without compromising other in-rubber properties, thus making the composites suitable for new demanding applications, such as energy harvesting. However, in most cases, surface modification of nanodiamonds requires the use of strong chemicals and high temperatures. The present study offers a less time-consuming functionalization method at 40 °C via reaction between the epoxy-rings of the modifier and carboxylic groups at the nanodiamond surface. This allows decorating the nanodiamond surface with chemical groups that are able to participate in the crosslinking reaction, thus creating strong interaction between filler and elastomer. Addition of 0.1 phr (parts per hundred rubber) of modified nanodiamonds into the silicone matrix results in about fivefold decreased electric losses at 1 Hz due to a reduced conductivity. Moreover, the mechanical hysteresis loss is reduced more than 50% and dynamic loss tangent at ambient temperature is lowered. Therefore, such materials are recommended for the dielectric energy harvesting application, and they are expected to increase its efficiency.

Removal of arsenic using functionalized cellulose nanofibrils from aqueous solutions

Cellulose nanofibrils (CNF) functionalized by introduction of trimethylammonium chloride were investigated for the uptake of arsenate [As(V)] from aqueous solutions. The modified-CNF was characterized using Energy Dispersive Spectrometry (EDS), argentometric titration, Boehr titration, zeta-potential, Scanning Electron Microscopy (SEM), Fourrier Transform Infrared (FTIR) spectroscopy, Nuclear Magnetic Resonance (NMR) spectroscopy, Brunauer-Emmet-Teller (BET), and Dynamic Light Scattering (DLS). The modified-CNF was effective for As(V) removal from laboratory and field samples. The As(V) adsorption was rapid and equilibrium was attained within two hours. The kinetic data were adequately described by the pseudo-second-order kinetics model suggesting that As(V) adsorption onto modified-CNF involves electrostatic forces and bonds between As(V) and adsorption sites. The adsorption isotherm data were well correlated with model. The modified-CNF exhibited an As(V) adsorption capacity (q_e) of approximately 25.5 mg g^-1. Competitive adsorption between As(V) and anions including NO₂^-, NO₃^-, and SO₄^2- was investigated and the results showed negligible influence on As(V) removal. However, PO₄^3- presence slightly reduced As(V) adsorption. Thermodynamics study showed that the As(V) adsorption onto modified-CNF is temperature dependent and is spontaneous and exothermic. Overall, the results of this study demonstrated that modified-CNF offers a propitious alterative for As(V) removal from water.

A Review on the Synthesis and Characterization of Biomass-Derived Carbons for Adsorption of Emerging Contaminants from Water

This review analyzes the preparation and characterization of biomass-derived carbons and their application as adsorbents of emerging contaminants from water. The study begins by identifying the different types of emerging contaminants more often found in water streams, including a brief reference to the available technologies for their removal. It also describes the biomass sources that could be used for the synthesis of biochars and activated carbons (AC). The characterization of the adsorbents and the different approaches that can be followed to learn about the adsorption processes are also detailed. Finally, the work reviews literature studies focused on the adsorption of emerging contaminants on biochars and activated carbons synthesized from biomass precursors.

Crucial Factors for the Application of Functional Nanoporous Carbon-Based Materials in Energy and Environmental Applications

This special issue of C—Journal of Carbon Research is dedicated to “Functional Nanoporous Carbon-Based Materials”. It contains contributions reporting on the synthesis of nanoporous carbons for the adsorption of proteins, their applications in electrochemical energy storage/conversion, and on the characterization/modification of their surface chemistry. Nanoporous carbon-based materials are widely researched, but at the same time, the field is still full of unutilized potential. The atomic construction of the carbon framework, pore sizes, pore geometries, presence of heteroatoms, particle size and shape, and many other “internal screws” are available; in the end, the high potential of carbon-based materials will only be fully explored if the interplay of these crucial factors is precisely controlled. This article is a summary of what we consider important for future targeted improvement of porous carbon nanomaterials for energy and environmental applications.

Boehm Titration Revisited (Part II): A Comparison of Boehm Titration with Other Analytical Techniques on the Quantification of Oxygen-Containing Surface Groups for a Variety of Carbon Materials

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.