High SSA Research Articles

Green synthesis of magnetic graphene-like biochar with oxygen vacancies for efficient adsorption and degradation of emerging antivirals from water

In this research, a magnetic biochar derived from the Vicia ervilia plant and possessing graphene-like properties (BC-G/Fe3O4) was used along with the activator persulfate for the adsorption and degradation of emerging pollutants such as Remdesivir and Favipiravir. The morphology, specific surface area, graphitization degree, and surface chemistry properties of the composite were determined using various techniques. The results showed that the synthesized BC-G/Fe3O4 had a high SSA (506.556 m2/g), indicating its suitable adsorption properties for the removal of antiviral drugs. The impact of various factors on the adsorption-oxidation process, including pH, catalyst dosage, oxidant concentration, antiviral concentration, and temperature, was examined and optimized through the utilization of response surface methodology and central composite design. The highest removal percentage of Remdesivir (93 %) and Favipiravir (98 %) was achieved at an initial antiviral concentration of 125 mg/L, catalyst dosage of 7 mg for Remdesivir and 5 mg for Favipiravir, contact time of 120 min, and pH of 7. Through the implementation of radical scavenging experiments, a thorough understanding of the mechanisms involved in PMS activation and the degradation of Favipiravir and Remdesivir was attained. The findings of this study indicate that the BC-G/Fe3O4 catalyst possesses excellent biocompatibility, adsorption-degradation capabilities, and reusability. Consequently, it can be successfully employed to eliminate emerging pollutants from aquatic environments.

Enzymatic depolymerization of polyester: Foaming as a pretreatment to increase specific surface area

AbstractPoly(ethylene terephthalate) (PET) is widely used for its high strength‐to‐weight ratio, gas barrier properties, and chemical resistance. The growing PET use highlights the demand for a better recycling system. Enzymatic recycling, alongside mechanical and chemical methods, is eco‐friendly and yields properties similar to virgin PET. Substrate properties (Tg, crystallinity, and specific surface area [SSA]) and enzyme stability significantly impact conversion efficiency. Higher SSA and lower crystallinity tend to yield improved depolymerization when employing leaf compost‐cutinase (LCC‐ICCG) enzymes. This study explored melt extrusion and foaming as pretreatment techniques to modify PET structural properties, using a low‐cost chemical foaming agent (CFA). The monomer conversion rate and efficiency during depolymerization were measured and related to the processing, extrudate micro‐ and meso‐structure, and polyester type. Pretreated PET substrates showed reduced Tg, crystallinity, density, and enhanced SSA, resulting in a 90% mass loss for foamed RPET and VPET substrates within 2 days. In contrast, PET with ~30% of cyclohexanedimethanol comonomer exhibited a nearly 50% lower depolymerization rate, with zero BHET production. It indicates that the combination of low crystallinity, low Tg, and high SSA leads to improved monomer conversion. These findings emphasize the significance of amorphization and foaming in enhancing PET enzymatic depolymerization.

Interplay of physical and textural properties in porous, nanostructured hard‑carbons as electrode materials for non-Faradic energy storage devices

This work presents a systematic investigation on the non-Faradic energy storage ability of non-graphitizable, porosity engineered hard‑carbon nanostructures as electrode materials. The persistent challenge of inducing and tuning porosity in hard‑carbon nanostructures is overcome here, by utilizing dendritic fibrous nano silica (DFNS) as a sacrificial template for uniform and conformal deposition of carbon through thermal chemical vapor deposition, leading to the formation of porosity tuned, nanostructured hard‑carbon florets (NCF). This strategy enables precisely crafted six varieties of NCF with varying yet monodisperse dimensions (NCF 90, NCF 350, NCF 366, NCF 430, NCF 540 and NCF 600), SSA (494–719 m2/g) and textural features such as pore volume (0.67–1.24 cm3/g) and pore diameter (3.83–5.65 nm). In contrast to current understanding, NCF 366 with defect length of 16 nm, defect density of 2.65 × 1011 cm−2, micro- to mesoscale pore ratio of 0.16 and specific surface area of 535 m2/g achieves the highest energy density of 14.6 Wh/kg and power density 10.0 kW/kg, when compared to NCF 90 with higher SSA (719 m2/g) and pore volume (1.24 cm3/g). Thus, this work manifests the critical contributions of tuning the pore structures and optimizing the relative contributions from multi-scale pore structures to achieve high-performing energy storage devices.

Design and construction of bio carbon derived Bi2Fe4O9 nanocomposites sensor for clad modified optical fiber sensors for detection of ethanol gas

Bio carbon (BC) derived Bi2Fe4O9 hybrid sensor was fabricated via sonochemical approach. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and N2 adsorption-desorption were used to determine the structural, morphological and porosity characteristics, respectively. The materials' gas-sensing properties were evaluated using a clad-modified optical fiber sensor. The orthorhombic structure with Pbam space group of Bi2Fe4O9 confirmed by the relative diffraction pattern. All sharp intense diffracted patterns might be indexed based on the standard value ((JCPDS card No. 74-1098). Both scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images illustrate those granular sheets with aggregated spherical shaped morphology of BC and Bi2Fe4O9, respectively. The pristine Bi2Fe4O9 exhibits Raman modes at 378 cm−1 and 617 cm−1, which is ascribed to the orthorhombic structure. The orthorhombic structure was already confirmed from XRD results. BFOG5 sample shows high SSA (107.5 m2/g) and pore size (38.4 nm), which is nearly 2.2 times greater than that of pristine Bi2Fe4O9 (54.3 m2/g and 23.4 nm). Fiber optic sensor was fabricated and tested for ethanol gas with various gas concentrations (0–500 ppm). The sensitivity (defined as slope of fitted line) enhanced from 14.69 (count/%) for bare Bi2Fe4O9 to 33.94 (count/%) for Bi2Fe4O9/BC (BFOG5). The response and recovery time was 25 s and 20 s for Bi2Fe4O9/BC (BFOG5) sensor, which is higher than that of bare Bi2Fe4O9 (42 s and 33 s). Our findings pave the way for a unique hybrid Bi2Fe4O9/BC composite to be used in a highly sensitive C2H5OH gas sensor system at RT.

Constructing the Interconnected and Hierarchical Nanoarchitectonics in Coal-Derived Carbon for High-Performance Supercapacitor.

Because of the deep and zigzag microporous structure, porous carbon materials exhibit inferior capacitive performance and sluggish electrochemical kinetics for supercapacitor electrode materials. Herein, a single-step carbonation and activation approach was utilized to synthesize coal-based porous carbon with an adjustable pore structure, using CaO as a hard template, KOH as an activator, and oxidized coal as precursors to carbon. The obtained sample possesses an interconnected and hierarchical porous structure, higher SSA (1060 m2 g-1), suitable mesopore volume (0.25 cm3 g-1), and abundant surface heteroatomic functional groups. Consequently, the synthesized carbon exhibits an exceptionally high specific capacitance of 323 F g-1 at 1 A g-1, along with 80.3% capacitance retention at 50 A g-1. The assembled two-electrode configuration demonstrates a remarkable capacitance retention of up to 95% and achieves Coulombic efficiency of nearly 100% with 10,000 cycles in a 6 M KOH electrolyte. Furthermore, the Zn-ion hybrid capacitor also exhibits a specific capacity of up to 139.1 mA h g-1 under conditions of 0.2 A g-1. This work offers a simple method in preparation of coal-based porous carbon with controllable pore structure.

Synthesis of novel maghemite (γ-Fe2O3)-decorated g-C3N4 nano-tubes (g-C3N4 NTs/γ-Fe2O3) photocatalytic nano-composite for ultrafast degradation of organics in wastewater: Insight into the mechanism of photoexcited charge separation

In this study, to enhance the photodegradation of organic pollutants including Methyl blue (MB) and Methyl orange (MO), mesoporous tubular g-C3N4/γ-Fe2O3 (FCN) nano-composite synthesized via facile procedures. FT-IR and XRD data proved the existence of maghemite (γ-Fe2O3) nanoparticles on the g-C3N4 nano-tubes. Experimental data showed that among fabricated photocatalysts, FCN exhibited the highest activity rate toward the photodegradation of MB (%96.1/60 min) and MO (%98.3/120 min) with an excellent kinetic rate of 0.0509 min−1 (MB) and 0.0352 min−1 (MO) under visible light and considerable photocatalytic stability after six cycles. In addition, the visible light-harvesting-capability of FCN enhanced compared to unequipped forms of g-C3N4 (BCN and CNNTs), surprisingly functioning under irradiation of photons greater than 900 nm, proving the synergistic role of γ-Fe2O3 nanoparticles not only in harvesting visible light but also in hindering electron-hole recombination. BET analysis showed mesoporous structure, the highest SSA and pore volume (55.623 m2/g, 0.1699 cm3/g) for FCN, indicating more active sites and enhanced target molecules adsorption, then augmented photocatalytic performance in comparison to the rest of the samples. Finally, FCN generated an excellent photocurrent density (3.76 μA/cm2) with the least arc radius, introducing a high-potential hybrid photocatalyst to the research field.

Pyrolysis polygeneration of the marine and terrestrial biomass and the chemical activation of bio-char as adsorbent to remove tetracycline hydrochloride from wastewater

Pyrolysis polygeneration is one of the promising approaches to convert biomass into bio-gas, bio-char, and bio-oil. In this work, the comparison of the properties of pyrolytic products from terrestrial biomass (poplar wood, PW) and marine biomass (microalgae, Chlorella vulgaris, CV) was carried out. Then, three types of activation agents (e.g., KOH, H3PO4, and ZnCl2) were used to improve the SSA and pore structure of bio-char for the removal of tetracycline hydrochloride (HTC) from wastewater. The yield of bio-char decreased with pyrolytic temperature increasing, while the yield of bio-gas increased. The yield of bio-oil reached the maximum value of 500 ºC. The yields of bio-gas and bio-char of CV were higher than that of PW at different temperatures, while the yield of bio-oil presented an opposite trend. Several nitrogenous chemicals were observed in pyrolytic bio-oil of CV due to thermal degradation of proteins. Among the three type of activation agents (H3PO4, KOH, and ZnCl2), KOH was the best activation agent to obtain activation carbon with highest SSA and pore volume. The CV-derived activated carbon by using KOH as activation agent presented highest specific surface area (1638.85 m2/g) and highest adsorption capacity of HTC (42.7 mg/g). Meanwhile, the CV-500-KOH still retained such high adsorption capacity of HTC (35.8 mg/g) after five cycles, suggesting that the N-doped bio-char possessed the excellent recyclability. In conclusion, compared to the PW-derived bio-char, CV-derived bio-char was a better precursor for production of activation carbon due to the higher N content in CV.

Married women’s decision-making autonomy on modern contraceptive use and its associated factors in high fertile sub-Saharan Africa countries: a multi-level analysis of Demographic and Health Surveys

BackgroundFor better maternal and child health, women’s independence on reproductive health issues is crucial; however, couples are restricted from discussing openly with their partner. Regarding this, information about women’s decision-making autonomy is low in the world, including Sub-Saharan Africa; therefore, this study was aimed to assess married women’s decision-making autonomy on modern contraceptive utilization in high fertility SSA countries.MethodsData for this study was obtained from the most recent (2010–2018) Demographic and Health Surveys. A total of weighted sample of 14,575 married reproductive age women was included. A multilevel mixed-effect binary logistic regression model was fitted to identify the significant associated factors of decision-making autonomy on modern contraceptive utilization. Finally, the Adjusted Odds Ratio (AOR) with 95% confidence interval was used to declare as statistical significance.ResultsOverall prevalence of married women decision-making autonomy on modern contraceptive utilization in the high fertile SSA countries is 25.28% (95% CI:18.32%, 32.24%). The factors significantly associated with the decision-making autonomy on modern contraceptive utilization were women’s age 25–34 years (AOR = 1.88, 95% CI = 1.84–1.93) and 35–49 years (AOR = 1.90, 95% CI = 1.82–1.92), had media exposure (AOR = 1.13, 95% CI = 1.00- 1.28), Number of alive children, 1–2 (AOR = 2.35, 95% CI = 1.38–4.01), 3–4 (AOR = 2.98, 95% CI = 1.74–5.10), ge 5 (AOR = 2. 82, 95% CI = 1.63–4.86), educational status; primary education (AOR = 1.93, 95% CI = 1.77–2.83), Secondary and higher (AOR = 2.11, 95% CI = 1.78–2.89), Community media exposure (AOR = 1.80, 95% CI = 1.38–2.34), Community level poverty, (AOR = 1.43, 95% CI = 1.09–1.86) and resides in rural (AOR = 0.67, 95% CI = 0.64–0.71).ConclusionWomen’s decision-making autonomy on modern contraception utilization in this study was low. Therefore, the government should promote women’s autonomy on contraceptive use as an essential component of SRH rights through mass media, with particular attention for, women living in the poorest communities, and those residing in rural settings of the country. Moreover, health professionals should counsel the women about the benefits of using modern contraceptive to help them managing their number of children.

Improvement of capacitor performance by pitch-based binder for a new alternative to polymer binders

Supercapacitors have gathered attention as one of the necessary energy storage devices. However, the use of polymer binder materials in the preparation of activated carbon-based electrodes hinders ion storage due to blocking the pore structure of activated carbons, and consequently causes reducing the electrochemical performance of EDLCs. We herein demonstrate the employment of pitch as an effective binder material for supercapacitors. The electrode using pitch binder shows a slight to decreased in specific surface area, managing to completely improve the electrochemical performance compared that PVDF binder. Such a fast and strong electrochemical performance ability of pitch-based electrodes are further investigated and verified by experimental and mechanism investigations. Benefitting from the synergistic effect exerts by a pitch in terms of EDLC, using pitch-based electrodes manifests excellent cycling and rate performances. Notably, the obtained pitch-based electrode with a high SSA of 1823 m2/g (PVDF electrode: 1,154 m2/g) delivers outstanding conductivity with 15.431 S/cm compared that a PVDF-based electrode has 6.118 S/cm. More importantly, a pitch-based binder electrode showed a remarkable capacitance of 410.6 mF/cm2 at 1 mA/cm2, as well as a favorable capacitance of 404.0 mF/cm2 after 10,000 cycles with a low-capacity decay of 1.6%. This report paves a practical route toward newly benign binder material design for high-performance EDLCs.

Facile synthesis of accordion-like porous carbon from waste PET bottles-based MIL-53(Al) and its application for high-performance Zn-ion capacitor

It is of great scientific and economic value to recycle waste poly (ethylene terephthalate) (PET) into high-value PET-based metal organic frameworks (MOFs) and further convert it into porous carbon for green energy storage applications. In the present study, a facile and cost-effective hydrothermal process was developed to direct recycle waste PET bottles into MIL-53(Al) with a 100% conversation, then the MOF-derived porous carbon was assembled into electrodes for high-performance supercapacitors. The results indicated that the as-synthesized carbon exhibited high SSA of 1712 m2 g−1 and unique accordion-like structure with hierarchical porosity. Benefit to these advantageous characters, the assembled three-electrode supercapacitor displayed high specific capacitances of 391 F g−1 at the current density of 0.5 A g−1 and good rate capability of 73.6% capacitance retention at 20 A g−1 in 6 mol L−1 KOH electrolyte. Furthermore, the assembled zinc ion capacitor still revealed outstanding capacitance of 335 F g−1 at 0.1 A g−1, excellent cycling stability of 92.2% capacitance retention after 10 000 cycles and ultra-high energy density of 150.3 Wh kg−1 at power density of 90 W kg−1 in 3 mol L−1 ZnSO4 electrolyte. It is believed that the current work provides a facile and effective strategy to recycle PET waste into high-valuable MOF, and further expands the applications of MOF-derived carbons for high-performance energy storage devices, so it is conducive to both pollution alleviation and sustainable economic development.

Synthesis of high purity magnesia MgO from Algerian dolomite ore

A nanometric Mg(OH)2 and MgO particles with high purity were successfully synthesized from Algerian dolomite via a leaching-precipitation-calcination process. The effect of leaching parameters, such as H2SO4 acid concentration (C), temperature (T), time (t), solid/liquid ratio (S/L), and precipitation parameters: type of precipitating base (KOH, NaOH, NH4OH), OH-/Mg2+ ratio, and temperature on the obtained product properties, were investigated using Taguchi approach. The optimal leaching conditions were selected as: C=5M, T=65?C, t=15 min, and S/L ratio=1:5. Furthermore, the potassium hydroxide (KOH) was selected as the optimal precipitating base with OH-/Mg2+ = 10.5. The calcination of the precipitates at 800?C during 2 h made it possible to produce a high purity MgO (~99.45 %) with a crystallite size of approximately 16.5 nm and particles in the form of agglomerated porous plates with a high SSA (70.42 m2/g) which may be of interest for some applications, such as catalysts or supports.

Low temperature in situ immobilization of nanoscale fcc and hcp polymorphic nickel particles in polymer-derived Si-C-O-N(H) to promote electrocatalytic water oxidation in alkaline media.

We synthesized nickel (Ni) nanoparticles (NPs) in a high specific surface area (SSA) p-block element-containing inorganic compound prepared via the polymer-derived ceramics (PDC) route to dispatch the obtained nanocomposite towards oxygen evolution reaction (OER). The in situ formation of Ni NPs in an amorphous silicon carboxynitride (Si-C-O-N(H)) matrix is allowed by the reactive blending of a polysilazane, NiCl2 and DMF followed by the subsequent thermolysis of the Ni : organosilicon polymer coordination complex at a temperature as low as 500 °C in flowing argon. The final nanocomposite displays a BET SSA as high as 311 m2 g-1 while the structure of the NPs corresponds to face-centred cubic (fcc) Ni along with interstitial-atom free (IAF) hexagonal close-packed (hcp) Ni as revealed by XRD. A closer look into the compound through FEG-SEM microscopy confirms the formation of pure metallic Ni, while HR-TEM imaging reveals the occurrence of Ni particles featuring a fcc phase and surrounded by carbon layers; thus, forming core-shell structures, along with Ni NPs in an IAF hcp phase. By considering that this newly synthesized material contains only Ni without doping (e.g., Fe) with a low mass loading (0.15 mg cm-2), it shows promising OER performances with an overpotential as low as 360 mV at 10 mA cm-2 according to the high SSA matrix, the presence of the IAF hcp Ni NPs and the development of core-shell structures. Given the simplicity, the flexibility, and the low cost of the proposed synthesis approach, this work opens the doors towards a new family of very active and stable high SSA nanocomposites made by the PDC route containing well dispersed and accessible non-noble transition metals for electrocatalysis applications.

Nitrogen doped carbonaceous materials as platinum free cathode electrocatalysts for oxygen reduction reaction (ORR)

Comparison of physicochemical properties and electrocatalytic behavior of different N-doped carbonaceous materials as potential catalysts for oxygen reduction reaction (ORR) was attended. Ball-milling of graphite with melamine and solvothermal treatment of graphite oxide, graphene nanoplatelets (GNP) with ammonia were used as preparation methods. Elemental analysis and N2 physisorption measurements revealed the synthesis of N-doped materials with strongly different morphological parameters. Contact angle measurements proved that all three samples had good wettability properties. According to analysis of XRD data and Raman spectra a higher nitrogen concentration corresponded to a smaller size of crystallites of the N-doped carbonaceous material. Surface total N content determined by XPS and bulk N content assessed by elemental analysis were close, indicating homogenous inclusion of N in all samples. Rotating disc electrode tests showed that these N-doped materials weremuch less active in acidic medium than in an alkaline environment. Although the presence of in-plane N species is regarded to be advantageous for the ORR activity, no particular correlation was found in these systems with any type of N species. According to Koutecky–Levich analysis, both the N-containing carbonaceous materials and the reference Pt/C catalyst displayed a typical one-step, four-electron ORR route. Both ball-milled sample with high N-content but with low SSA and solvothermally synthesized N-GNP with high SSA but low N content showed significant ORR activity. It could be concluded that beside the total N content other parameters such as SSA, pore structure, structural defects, wettability were also essential for achieving high ORR activity.

Long acting reversible contraceptive utilization and its associated factors among modern contraceptive users in high fertility sub-Saharan Africa countries: a multi-level analysis of recent demographic and health surveys

BackgroundLong-acting reversible contraceptives (LARC) have been hailed as one of the safest and most effective methods of contraception. However, the use of LARC is low in the world, including Sub Saharan Africa; therefore, the aim of this study was to assess LARC utilization and associated factors among modern contraceptive users in high fertility SSA countries.MethodsData for this study was obtained from the most recent Demographic and Health Surveys. A total weighted sample of 14,828 reproductive age women was included. A multilevel mixed-effect binary logistic regression model was fitted to identify the significant associated factors of long acting reversible contraception utilization. Finally, the Adjusted Odds Ratio (AOR) with 95% confidence interval was used to declare as statistical significance.ResultsOverall prevalence of LARC utilization was observed to be 20.1% (19.45, 20.74). The factors significantly associated with the utilization were women’s age ≥ 35 years (AOR = 1.42; 95% CI: 1.19,1.68), having media exposure (AOR = 1.13; 95% CI: 1.05, 1.28), number of alive children: 1–2 (AOR = 2.35; 95% CI: 1.38, 4.01), 3–4 (AOR = 2.98; 95% CI: 1.74, 5.10), ge 5 (AOR = 2.82; 95% CI:1.63, 4.86), have no history of abortion (AOR = 1.33; 95% CI: 1.17,1.51) and who have no big problem with distance to the health facility (AOR = 1.29; 95% CI: 1.16, 1.43).ConclusionThe use of long acting reversible contraception in this study was relatively low. To improve the utilization of long acting reversible contraceptives governments, policymakers, and stakeholders should implement health promotion strategies through media and improve accessibilities of health facilities.

Molten salt synthesis of nitrogen-doped hierarchical porous carbon from plantain peels for high-performance supercapacitor

• A green and scalable molten salt method is employed to synthesize hierarchical porous carbon from plantain peels. • A high SSA of 959 m 2 /g, interconnected pore structure and highly defective and graphitized framework obtained. • The N -doped porous carbon exhibited high specific capacitance of 550 F/g at a current density of 1 A/g in a three-electrode setup. • Capacitance retention of 99% after 1000 cycles at 4 A/g This work employs a non-corrosive and non-toxic molten salt combination of NaCl and KCl as an activation agent in an air environment to synthesize nitrogen-doped hierarchical porous carbon from plantain peels at 800 °C for supercapacitor application. Due to the synergistic effect of nitrogen doping, the synthesized nitrogen-doped activated unripe porous carbon (AUPN) has a hierarchical (micro-meso-macropores) porous structure and a high surface area of 959 m 2 /g, providing sufficient active sites for charge storage, rapid electrolyte and ionic mobility. X-ray diffraction and Raman spectroscopy analysis revealed the formation of a carbon product with a limited degree of graphitization and the crystallite size (L a ), which is valuable for evaluating the defects caused by nitrogen doping. In a three-electrode cell with a 6 M KOH electrolyte, AUPN recorded a specific capacitance of 550 F/g at 1 A/g. After 1000 cycles, capacitance retention was 99% at 4 A/g. Compared to other reported porous carbon materials, the overall electrochemical performance of AUPN is superior. This is due to the abundant nitrogen-doping, which introduces pseudocapacitance and increases the surface wettability of the porous carbon, resulting in a decrease in ionic-transport resistance. These findings indicate that this green and scalable technique is a potential synthesis method for producing porous carbon materials for energy storage applications.

Rice husk derived capacitive carbon prepared by one-step molten salt carbonization for supercapacitors

High-performance carbonaceous electrode materials for supercapacitor were prepared via a simple molten salt carbonization of rice husk in molten eutectic Na2CO3-K2CO3 at 850 °C. Carbon material with carbonization time of 12 h exhibits an ideal capacitive property, benefitting from the synergistic effect of hierarchically porous structure with high SSA and mesopore/micropore ratio, oxygen doping and excellent electrical conductivity. In a three-electrode system, it exhibits specific capacitance of 117.0–163.1 F g−1 at current density of 20–0.2 A g−1 with rate performance of 72 % capacitance retention, energy (power) density of 22.6 Wh kg−1 (99.9 W kg−1) at 0.2 A g−1 and power (energy) density of 9.5 kW kg−1 (14.5 Wh kg−1) at 20 A g−1. When the carbon material was assembled into a symmetrical supercapacitor, it exhibits specific capacitance of 103.4–148.3 F g−1 at current density of 20–0.2 A g−1 with rate performance of 70 % capacitance retention, energy (power) density of 5.1 Wh kg−1 (49.9 W kg−1) at 0.2 A g−1 and power (energy) density of 4.3 kW kg−1 (2.7 Wh kg−1) at 20 A g−1, as well as excellent cyclic stability with 85 % capacitance retention and the coulombic efficiency close to 100 % after 6000 charge-discharge cycles at 1 A g−1. The dependence of hierarchically porous structure on capacitive performance is also discussed.

Study and Comparison of Different Routes to Synthesize Reduced Graphene Oxide

The feasibility of graphene oxide (GO) obtained by both Hummers and Tour method to prepare reduced graphene oxide (rGO) as well as chemically reduction under different experimental conditions were evaluated with the objective of establishing the key items that should be considered when performing the synthesis of GO and rGO. This key items can be supportive to select the most feasible methodology to synthesize GO and rGO depending on the future application. Reduced graphene oxide was prepared by combining chemical and solvothermal as well as combined reduction adding a final thermal annealing step. Obtained GO and rGO were characterized by XRD, Raman spectroscopy, XPS and BET analysis. A higher oxidation degree was achieved for samples from Tour method than those oxidized by Hummers method. On the contrary, lower oxidation degree from Hummers graphene oxide (GO-H) facilitates the subsequent reduction process, leading to a higher reduced rGO. Hence, rGO samples obtained from the Hummers method in the different reduction treatments presented higher C/O atomic ratios than the corresponding Tour method. In addition, the combination of a solvothermal treatment and chemical reduction, including a final annealing stage, increases significantly the value of the C/O ratio as well as it contributes to decrease the defect density and the restoration of π-conjugated structure. Besides, rGO samples obtained from Tour method presented higher SSA and pore volume than those samples obtained from Hummers method. Results from this study suggest the suitability of Tour graphene oxide (GO-T) for chemical functionalization which is very useful for several applications. In addition, GO and rGO coming from Tour method are more appropriate to applications in which high surface area is required. Taking into account the vast possible applications for chemically-exfoliated graphene the findings of this study could help to select the best method for oxidising graphite depending on the intended application.

Porosity and crystallinity dynamics of carbon black during internal and surface oxidation

The structure of carbon black (CB) is investigated during its oxidation by O2 at 550 and 800 °C by thermogravimetric analysis, microscopy, N2 adsorption and X-ray diffraction (XRD). That way, the dynamics of its porosity and crystallinity during surface and internal oxidation are elucidated, for the first time to the best of our knowledge. At 800 °C, oxidation takes place largely on the CB surface. This increases the CB specific surface area, SSA, from 240 to about 453 m2/g, closely following the classic shrinking particle model and hardly affects the porosity and crystallinity of CB. At 550 °C, O2 diffuses and reacts with the bulk of CB particles forming pores with radius smaller than 2 nm after 25 and 50% conversion. At higher conversions, these small pores fuse together resulting in hollow CB particles with high SSA, up to 939 m2/g. Fractal and XRD analyses of the resulting pore network reveals that internal oxidation at 550 °C reduces the interlayer distance of the crystallites constituting the CB, compacting its pore network. This increases the pore fractal dimension, Dfp, from 2.43 up to about 2.7, in good agreement with the Dfp measured during diesel soot oxidation. The dynamics of CB porosity and crystallinity quantified in detail here can assist the design of new highly porous CB grades and activated carbons as well as battery materials.

Novel MOF-808 metal–organic framework as highly efficient adsorbent of perfluorooctane sulfonate in water

Perfluorooctane sulfonate (PFOS) is a highly persistent contaminant of emerging concern causing harmful effects to human and ecosystem health. In this study, a novel MOF-808 metal–organic framework (MOF) was prepared and evaluated for adsorptive removal of PFOS from aqueous solution. The MOF-808 had high specific surface area (SSA; 1610 m2/g) and was structurally stable in aqueous medium for 7 days under different pH conditions. The MOF-808 reached PFOS adsorption equilibrium within 30 min (at 500 mg/L initial PFOS) and attained the maximum adsorption capacity of 939 mg/g at pH 4.1 – 5.4 (with 50 – 500 mg/L initial PFOS). The PFOS adsorption capacity of MOF-808 was unaffected at pH 2 to 7, but gradually decreased at pH > 7. High SSA, favorable pore size and abundant active adsorption sites on MOF-808 triggered high PFOS adsorption onto the adsorbent. The PFOS adsorption process was endothermic and spontaneous in nature. Electrostatic interaction between the cationic central cluster ([Zr6O4(OH)4]12+) of MOF-808 and PFOS anion was identified as the key mechanism of PFOS adsorption onto MOF-808, as evident from the infrared spectroscopic investigation of the adsorbent. This study suggests that MOF-808 can be considered as a highly efficient adsorbent for PFOS removal from water and warrants future research to evaluate the application and performance of the material under wastewater conditions.

Study of mechanical, durability and microstructural properties of cementitious composite with addition of different iron ore tailings from Brazil

Brazil is the second-largest global iron ore producer in the world. Consequently, a large volume of iron ore tailings (IOTs) is generated, which is associated with environmental impacts. IOTs present potential to be used as an addition in cementitious compounds, however, few studies assess how the heterogeneity of this waste can limit its utilization as a building material. Thus, the present study aims to assess whether the heterogeneity of IOTs influences mechanical, durability, and microstructural properties when added to the cementitious composite. Four IOTs samples from different origins were collected and added to cementitious composite at 40% addition content. Composites’ mechanical (compressive strength and modulus of elasticity) and durability properties (water absorption, porosity, electrical resistivity, carbonation, and pH pore solution) were correlated to the microstructure of the IOTs. Results showed that the IOTs from different mines exhibited different physical properties and chemical/mineralogical compositions. Moreover, the higher the degree of ore processing, the lower the heterogeneity, iron content, and specific gravity. Although the IOT samples are heterogeneous, this type of tailing can be used as a filler addition in structural mortars. IOT addition tends to improve the mechanical and durability properties. Heterogeneity most significantly influenced the properties in the fresh state, durability, and microstructural properties. The microstructure of the cement matrix tends to be denser in the IOT-added with higher SSA and silica content. Was observed higher-porosity in regions close to the interfacial transition zone in the samples with coarser IOT.