1-D Carbon Nano-Coils Derived from Almond Skin: Exhibiting Density of State, Diffusivity, Electron Transfer Rate, and Dopamine Redox Modulation Properties Akin to Graphene Oxide.

The quest to develop graphene-like biomass-carbon for advanced biomolecule redox modulation and sensing remains a challenge. The primary obstacle is the limited ability of biomass to undergo extensive graphitization during pyrolysis resulting in the formation of amorphous carbon materials with a small carbon-double-bond-carbon domain size (Lsp2 ), density of state (LDOS), ion diffusivity (D), and electron transfer rate constant (Ks). Herein, using almond skin (AS) the morphology of biomass is demonstrated as the key to overcoming these limitations. AS consists of 1D syringyl/guaiacyl lignin nano-coils which under H2 /H2 annealing transform into pyrolytic 1D carbon nano-coils (r-gC). Spectroscopy and microscopy analyses reveal that the sheet layering structure, crystallinity, LDOS, and Lsp2 of r-gC mimic those of graphene oxide (GO). Moreover, its unique 1D morphology and profound microstructure facilitate faster charge transfer and ion diffusion than GO's planar structure, leading to better redox modulation and sensing of the neurotransmitter dopamine (DA) in physiological fluids. r-gC's DA detection limit of 3.62 nM is below the lower threshold found in humans and on par with the state-of-the-art. r-gC is also DA-selective over 14 biochemicals. This study reveals that biomasses with well-defined and compact lignin structures are best suited for developing highly electroactive graphene-like biomass carbon.

Preparation and Characterization of Palmitoyl Grafted Cellulose Nano Absorbent for the Efficient Adsorption of Pyrene from Aqueous Solution.

Palmitoyl grafted modified cellulose were prepared by simple chemical grafting method and applied as nano adsorbent for removal of pyrene from aqueous solution. The chemical properties and morphology of prepared nano-adsorbent were characterized by FT-IR, XRD, SEM, EDX, TGA, and contact angle. Results showed that palmitoyl successfully grafted on the surface of cellulose and possess effective organic functional groups for the adsorption of pyrene from aqueous solution. The adsorption performance of modified cellulose was significantly improved toward pyrene in aqueous solution. It is worthy to note that 0.25 g of palmitoyl grafted cellulose (PMC) removed 92% pyrene compared to unmodified cellulose which adsorbed 36% pyrene from 1.65 ppm aqueous solution of pyrene in very short contact time at room temperature. Results showed that, presence of various organic functional groups from palmitoyl chains grafted on cellulose backbone affected to pyrene removal. After completion of adsorption phenomenon nano-adsorbent can be removed by simply filtration process and reused several times. The adsorption capacity was studied under different experimental conditions and their effects on adsorption such as temperature, pH, and contact time were also studied. The kinetics and isotherms of material were also determined.

Leveraging Direct Pyrolysis for the Synthesis of 10†nm Monodispersed Fe3O4/Fe3C NPS@Carbon to Improve SupercapacitANCE in Acidic Electrolyte.

The prevailing practice advocates pre-oxidation of electrospun Fe-salt/polymer nanofibers (Fe-salt/polymer Nf) before pyrolysis as advantageous in the production of high-performance FeOx@carbon nanofibers supercapacitors (FeOx@C). However, our study systematically challenges this notion by demonstrating that pre-oxidation facilitates the formation of polydispersed and large FeOx nanoparticles (FeOx@CI-DA) through "external" Fe3+ Kirkendall diffusion from carbon, resulting in subpar electrochemical properties. To address this, direct pyrolysis of Fe-salt/polymer Nf is proposed, promoting "internal" Fe3+ Kirkendall diffusion within carbon and providing substantial physical confinement, leading to the formation of monodispersed and small FeOx nanoparticles (FeOx@CDA). In 1 M H2SO4, FeOx@CDA demonstrates ~2.60× and 1.26× faster SO4 2- diffusivity, and electron transfer kinetics, respectively, compared to FeOx@CI-DA, with a correspondingly ~1.50× greater effective surface area. Consequently, FeOx@CDA exhibits a specific capacity of 161.92 mAhg-1, ~2× higher than FeOx@CI-DA, with a rate capability ~19 % greater. Moreover, FeOx@CDA retains 94 % of its capacitance after 5000 GCD cycles, delivering an energy density of 26.68 Whkg-1 in a FeOx@CDA//FeOx@CDA device, rivaling state-of-the-art FeOx/carbon electrodes in less Fe-corrosive electrolytes. However, it is worth noting that the effectiveness of direct pyrolysis is contingent upon hydrated Fe-salt. These findings reveal a straightforward approach to enhancing the supercapacitance of FeOx@C materials.

Engineering FeOOH/Fe2O3@Carbon Interfaces with Biomass-Derived Carbon Nanodot/Iron Colloids for Efficient Redox-Modulated Dopamine Voltammetric Detection.

The Fe2+/Fe3+ redox couple is effective for voltammetric detection of trace dopamine (DA). However, achieving adequate concentrations with high electroactive surface area (ECSA), DA affinity, and fast interfacial charge transfer is challenging. Consequently, most reported Fe-based sensors have a high nanomolar range detection limit (LOD). Herein, we address these limitations by manipulating the phase and morphology of FeOOH/Fe2O3 heterojunctions anchored on sp2-carbon. FeOOH/Fe2O3 is synthesized by variable temperature aging of unique Fe5H9O15/Fe2O3@sp2-carbon colloidal nanoparticles, which form via chelation between biomass-derived carbon nanodots (CNDs) and Fe2+ ions. At 27°C and 120°C, Fe5H9O15/Fe2O3@sp2-carbon transforms into ß-FeOOH/Fe2O3 nanoparticles and α-FeOOH/Fe2O3 nanosheet, respectively. The ß-FeOOH/Fe2O3 interface exhibits higher eg orbital electron occupancy than α-FeOOH/Fe2O3, thereby facilitating oxygen adsorption and the generation of Fe2+/Fe3+ sites near the polarization potential of DA. This facilitates interfacial electron transfer between Fe3+ and DA. Moreover, its nanoparticle morphology enhances ECSA and DA adsorption compared to α-FeOOH/Fe2O3 nanosheets. With a LOD of ~3.11 nM, ß-FeOOH/Fe2O3 surpasses the lower threshold in humans (~10 nM) and matches noble-metal sensors. Furthermore, it exhibits selective detection of DA over 10 biochemicals in urine. Therefore, the ß-FeOOH/Fe2O3@sp2-C platform holds promise as a low-cost, easy-to-synthesize, and practical voltammetric DA monitor.

Electrochemically engineered zinc(iron)oxyhydroxide/zinc ferrite heterostructure with interfacial microstructure and hydrophilicity ideal for supercapacitors.

Zinc ferrite@nickel foam (ZF@Nf) is a potential commercial supercapacitor electrode due to its large theoretical capacity, abundant elemental composition, excellent conductivity, and stability. However, deficient active sites limit its specific capacitance (SC). Herein, we demonstrate that engineering ZF's interfacial microstructure and hydrophilicity mitigate this limitation. ZF@Nf is used as the working electrode in a 3-electrode cell and subjected to multiple oxygen evolution reaction cycles in potassium hydroxide. Systematic changes in ZF's porosity, crystallinity, hydrophilicity, and composition after each cycle were characterised using spectroscopy, sorption isotherm, microscopy and photography techniques. During cycling, the edges of ZF partially phase-transform into a dense polycrystalline zinc(iron)oxyhydroxide film via semi-reversible oxidation resulting in zinc(iron)oxyhydroxide/ZF interface formation. The maximum ion-accessible zinc(iron)oxyhydroxide film density is obtained after 1000 cycles. Strong ionic interaction at the interface induces high hydrophilicity, this together with the 3-dimensional diffusion channels of the zinc(iron)oxyhydroxide significantly increase electroactive surface area and decrease ion diffusion resistance. Consequently, the SC, energy density, and rate-capability of the interface compare favourably with state-of-the-art electrodes. The strong interfacial interaction and polycrystallinity also ensure long-term electrochemical stability. This study proves the direct correlation between interfacial microstructure and hydrophilicity, and SC which provides a blueprint for future energy-storage electrode design.

Ground coffee waste-derived carbon for adsorptive removal of caffeine: Effect of surface chemistry and porous structure.

Carbon-based adsorbents show high adsorption capacity towards caffeine due to their porosity and surface functionality. However, the main limiting factor for high performance has not been addressed; furthermore, the adsorption interaction with different active sites needs to be explored. In this study, we synthesized a hierarchical porous nitrogen-doped carbon with unique surface functionality by single-step calcination of coffee waste with KOH under N2. The porous structure, nitrogen content, and types are optimized by varying calcination temperature and KOH concentration. The result of the adsorption experiments shows that both the nitrogen type and the pore size distribution are the limiting factors to adsorption. In addition, the effect of acidic and basic functional groups is studied in detail. The adsorption of caffeine on CW-C is dominantly governed by EDA interaction between the resonance structure of pyridonic-N and the electron-withdrawing group of the caffeine, and the dispersive force caused by the oxidized-N and delocalized π electron of caffeine. Furthermore, we demonstrate that the surface of CW-C is not suitable for the formation of electrostatic and non-electrostatic interaction with caffeine. The maximum adsorption capacity of caffeine at 25 °C is 274.2 mg/g. Moreover, we demonstrate that the unique physio-chemical properties of CW-C are capable of adsorbing other emerging contaminants such as diclofenac, where maximum adsorption capacity of 242.3 mg/g diclofenac is recorded.

Azo-dye derived oxidized-nitrogen rich carbon sheets with high adsorption capability for dye effluent under both batch and continuous conditions.

The removal of methyl blue (MB) from wastewater using graphene and its derivative is very successful due to their high aromaticity which drives adsorption via π-π and electron-donor-acceptor (EDA) interactions; however, graphene is expensive and difficult to synthesize, which limit its practical application. Meanwhile, low aromatic carbon materials (LACM) derived from farm-water and other materials are cheaper and easier to synthesize but have limited π-π and EDA interactions and low adsorption capacity. Herein, we demonstrate that LACM with oxidized-nitrogen (N-O-) functionality overcomes this limitation via chemisorption of MB through a combination of hydrophobic-hydrophobic interactions and EDA interactions. This is confirmed using XPS analysis of LACM/N-O- post MB adsorption. Consequently, a remarkable adsorption capacity of 3904 mg g-1 is achieved under batch condition which is the highest ever reported for any MB adsorbent. Furthermore, LACM/N-O- works equally well under continuous-flow adsorption conditions which shows its practicability. Amongst several LACM precursors tested, only Azo-dyes are able to generate LACM/N-O- implying that the NN moiety is key to N-O- formation. A carbonization temperature of 700 °C generates the highest N-O- sites hence the highest adsorption capacity. Characterization of LACM/N-O- is done mainly using BET, XPS, Raman, TGA, and FTIR analysis.

Gallic acid modified alginate self-adhesive hydrogel for strain responsive transdermal delivery.

Transdermal drug delivery (TDD) has gained attention over the past decades as a pain-free drug administration path. Various drug release control mechanisms have also been developed for the advanced application of TDD. However, most controlled delivery systems depend on external stimuli such as temperature, pH and so on; making the design complicated and more expensive. In this study, we prepared mussel inspired self-adhesive hydrogel for monolith, drug in adhesive, strain-controlled transdermal delivery using a simple and effective method. The synthesis method involves modifying alginate with gallic acid followed by in-situ polymerization of polyacrylic acid. The resulting hydrogel (GA) is a heavily intertwined, interpenetrating supramolecular network mainly due to the numerous hydrogen bonds. It is extremely stretchable (800% strain) and adheres strongly on polymer, glass, and metal under both wet and dry conditions. Additionally, it has a layered and highly porous internal structure providing excellent elasticity and efficient drug delivery. Kinetic experiment results show that 77.47%, 82.09%, 87.64% and 42.54% of pre-loaded caffeine in GA is released within an hour under 100%, 50%, 25%, and 0% tensile strain, respectively. These results demonstrate that GA is a potential self-adhesive matrix for strain controlled TDD for caffeine possibly for other drugs as well.

Synergism of transition metal (Co, Ni, Fe, Mn) nanoparticles and "active support" Fe3O4@C for catalytic reduction of 4-nitrophenol.

Research reports, up to date, on supports for non-noble metal catalyst focus mainly on tuning their surface functionality and increasing surface area to maximize metal loading for high catalytic reduction of 4-nitrophenol. However, the "passive" role of these supports leads to inefficient hydride formation on the metal surface which limits catalytic activity. Herein, we present Fe3O4@porous-conductive carbon (Fe3O4@C-A) core-shell structure as an "active" support for non-noble metals (M = Co, Ni, Fe, and Mn) nanoparticles. Fe3O4@C-A was prepared by annealing Fe3O4@dense-carbon (Fe3O4@C) under N2. The resultant M-Fe3O4@C-A catalysts show high catalytic performance at very low metal loading, while non-noble metals supported on a "passive" support (Fe3O4@C) shows very low activity even at high metal loading. The significant difference in catalytic activity is ascribed to the synergistic effect amongst Fe3O4, conductive carbon and metal nanoparticles which leads to efficient hydride formation. Amongst the prepared catalysts, Ni-Fe3O4@C-A and Co-Fe3O4@C-A show the best catalytic activity, completing 4-nitrophenol reduction within 50 s and 80 s, respectively, in the presence of NaBH4. This result is comparable with previously reported noble-metal-based nanocomposites. In addition, Co-Fe3O4@C-A shows high recyclability in 5 consecutive catalytic reactions. In the broader context, our finding highlights how an "active support" together with non-noble metals can provide an efficient mechanism for hydride formation, subsequently accelerating the catalytic reduction of 4-nitrophenol.

Tuning the charge carrier density and exciton pair separation in electrospun 1D ZnO-C composite nanofibers and its effect on photodegradation of emerging contaminants.

Maximizing anion (carbon) doping is thought to increase the charge carrier density in ZnO and other semiconductor metal oxide photocatalysts. It also enhances the photocatalytic activity of ZnO nanostructures by imparting visible light responsiveness. However, the effect of the carbon source on the doping efficiency, and in turn on the photocatalytic activity of ZnO nanostructures has been overlooked thus far. In this study one dimensional (1D) ZnO-Carbon composite nanofibers were prepared from different polymer (polyacrylonitrile, polystyrene, polyvinylpyrrolidone) precursor solutions and the C-doping efficiency and its effect on the photocatalytic activity were studied. The prepared nanofiber photocatalysts were characterized by XRD, XPS, FE-SEM, BET, TGA, FT-IR, photoelectrochemical and optical analyses techniques. Based on the thermal degradation profile of the polymer sources, the C-doping efficiencies varied among the samples prepared and so does their photocatalytic activity. Caffeine molecule was selected as a model emerging contaminant and its photodegradation was analyzed in the presence of the as-prepared photocatalysts. Upon the C-doping, new energy level was introduced within the bandgap of ZnO that lowers its bandgap energy by 0.35 eV. Additionally, the charge carrier density of ZnO increased and the flat band potential showed positive shift. These, together with the 1D nature of the photocatalysts, enhanced the photocatalytic activity of pristine ZnO by ~58% and 2.8 folds faster kinetics. Mechanistic study showed that hydroxyl radicals were the most active reactive species responsible for the caffeine molecule degradation. This study underscores that the photocatalytic activity of ZnO for the degradation of environmental pollutants can be maximized by C-doping through careful selection of the carbon source.

Amorphous iron sulfide nanowires as an efficient adsorbent for toxic dye effluents remediation.

Environmental and health concerns arising from the toxicity of organic dye effluents is still the issue of the twenty-first century. In that regard, this study presents iron sulfide (FeS2) for its use in environmental remediation application. Amorphous phase FeS2 nanowires were synthesized by PVP-assisted solvothermal reaction and were characterized using XRD, XPS, BET, FE-SEM, and EDS techniques. The amorphous phase FeS2 is attractive from material synthesis point of view as its synthesis does not require delicate control over the process parameters, unlike the crystalline phase. The 1-D nanowire FeS2 had a high surface-to-volume ratio with negative zeta potential within a wide pH range. Having those surface and microstructural properties, these nanowires exhibited excellent adsorption property towards model organic dyes, Congo red (anionic), and methylene blue (cationic), with theoretical adsorption capacity of 118.86 and 48.82 mg g-1, respectively. Adsorption kinetics and isotherm models were implemented to study the adsorption processes at different adsorption conditions (pH, adsorbent loading, initial adsorbate concentration). The pH dependence of the adsorption and FT-IR analysis evidenced the prevalence of both physisorption and chemisorption during the adsorption of Congo red. Recyclability test proved the excellent performance of this amorphous FeS2 nanowire adsorbent for three consecutive cycles. Considering its ease of synthesis, excellent adsorption property, and cyclic performance, the as-prepared adsorbent could be a promising material for dye effluents treatment.

In-situ prepared ZnO-ZnFe2O4 with 1-D nanofiber network structure: An effective adsorbent for toxic dye effluent treatment.

Current research on ZnFe2O4-based adsorbents rely mainly on its surface charge to remove Congo red (CR). However, the weak charge of ZnFe2O4 due its normal spinel structure makes this approach inefficient as evident from its low activity. Considering the potential of ZnFe2O4 as a low cost nontoxic adsorbent, it is important to improve its activity. Herein, we present an in-situ prepared 1-D ZnO-ZnFe2O4 with a heterojunction which adsorbs CR chemically instead of the generic physisorption. While its 1-D structure allows very low adsorbent loading to be employed. Together, these two unique properties make 1-D ZnO-ZnFe2O4 ˜3.3x more effective at treating CR effluent than reported ZnFe2O4-based adsorbents. The chemisorption reaction involves chelating/bridging bidentate bonding between sulfonic groups on CR and ZnO-ZnFe2O4 heterojunction. Its potency is regulated by the ZnO content of the composite which suggest a synergistic effect between the metal oxides phases. Interestingly, spent 1-D ZnO-ZnFe2O4 can be regenerated in NaOH solution and retains ˜75% of its adsorption capacity even after repeated use. These findings provide key insights into how interfacial interactions in mixed metal oxide composites and their morphology affect dye adsorption. This information may be useful to develop high performing adsorbents from metal oxides in general.

Engineered iron-carbon-cobalt (Fe3O4@C-Co) core-shell composite with synergistic catalytic properties towards hydrogen generation via NaBH4 hydrolysis.

Cobalt (Co) nanoparticle supported catalysts have better dispersion and recyclability than unsupported Co. However, the surface chemistry and limited surface area (SA) of supports limit their Co loading which lowers activity. Currently, supports with high SA and functionality which allow high Co loading are been developed. However, a smarter solution would be to develop "active" supports which can boost the activity of Co, even at low loading. The value of such a support lies in the ability to use low catalyst loading without scarifying activity. Herein, we demonstrate how via a simple annealing process the chemical properties of Fe3O4 and physico-electrical properties of carbon (C) in Fe3O4@C can be effectively combined to prepare an "active" support for Co. The unique properties of the "active" Fe3O4@C triggers a synergistic catalytic reaction involving Co, Fe3O4 and C during NaBH4 hydrolysis. Consequently, the hydrogen generation rate (1746 ml g-1 min-1) and activation energy (47.3 kJ mol-1) of Fe3O4@C-Co are significantly enhanced compared to reported catalyst even though its Co loading is significantly lower. Additionally, Fe3O4@C-Co is highly recyclable which demonstrates its stability. Our study gives a new perspective on the role supports can play in catalyst design.

A Simple Method of Electrospun Tungsten Trioxide Nanofibers with Enhanced Visible-Light Photocatalytic Activity.

The present study involves the fabrication of tungsten trioxide (WO3) nanofibers by an electrospinning technique using polyvinyl pyrrolidone (PVP)/citric acid/tungstic acid as precursor solution. It was found that the PVP concentration was one of the most crucial processing parameters determining the final properties of WO3 nanofibers. The optimum concentration of PVP was from 75 to 94 g L-1. The average diameter of the nanofibers increases with increasing the PVP concentration, whereas it is decreased after sintering and orthorhombic structure were formed at 500 °C. The photocatalytic properties of the as-synthesized nanofibers were also investigated by degrading methylene blue and twofold efficiency was obtained compared with that of commercial WO3 microparticles.