Isolation, Oxidation, and Application of Crystalline-Pristine Cellulose: Natural Products That Could End Plastic Waste.

ConspectusGiven this special issue's efforts to highlight the research emanating from HBCUs (Historically Black Colleges and Universities) and the trials and tribulations associated with their research, the authors have presented work associated with the characterization and application of cellulosic materials as renewable products. Despite challenges, the research completed in this laboratory at Tuskegee, a HBCU, hinges upon the many investigations of cellulose as a carbon-neutral, biorenewable material that can potentially replace environmentally unfriendly and hazardous petroleum-based polymers. Although cellulose is one of the most promising candidates, overcoming the challenge of its incompatibility (i.e., lack of good dispersion, interfacial adhesion, etc.) with most hydrophobic polymers due to its hydrophilic nature is critical to usage in plastic products across industries. Chemical isolations via acid hydrolysis and surface functionalities have emerged as new approaches to modulate the surface chemistry of cellulose to improve its compatibility and physical performance within the polymer composites. Recently, we have explored the influence of (1) acid hydrolysis and (2) chemical modifications via surface oxidation to ketones and aldehydes on the resulting macrostructural arrangements and thermal performance and (3) the application of crystalline cellulose as reinforcement agents in ABS (acrylonitrile-butadiene-styrene) composites.XRD structural characterizations of crystalline cellulose isolated from wheat straw under dissimilar acid hydrolysis conditions showed induced alterations in the native cellulose polymorph (CI). Mixing of the native polymorph (CI) with CIII was observed and found to be more prominent under sulfuric acid isolation conditions which is one of the more commonly used methods of chemical isolation. Thermal evaluations using TGA confirmed that the introduction of the mixed polymorphs changed the thermal behavior of the isolated crystalline cellulose. Further, FTIR analysis and Tollens testing of chemically oxidized crystalline cellulose via the Albright-Goldman reaction revealed the transformation of surface OH groups to ketones and aldehydes, respectively. We observed similar macrostructural disruption behavior to that of acid hydrolysis processing (i.e., mixing of polymorphs) for oxidation of crystalline cellulose, which had no negative impacts on the thermal stability of the cellulosic structure. The application of acid-hydrolyzed pristine cellulose (PC) as reinforcement agents in ABS composites showed increased thermal-mechanical performance as revealed by TGA and thermal mechanical analysis (TMA). As the ratio of crystalline cellulose increased, the thermal stability of the ABS composite increased, and at extremely high ratios, increased dimensional stability (i.e., low coefficient of thermal expansion (CTE) value) was observed, expanding the application of ABS plastic products.

Tuning the Intermolecular Electron Transfer of Low-Dimensional and Metal-Free BCN/C60 Electrocatalysts via Interfacial Defects for Efficient Hydrogen and Oxygen Electrochemistry.

The development of low-dimensional (LD) supramolecular materials with multifunctional electrocatalytic properties has sparked the attention of the catalysis community. Herein, we report the synthesis of a new class of 0D-2D heterostructures composed of boron carbon nitride nanosheets (BCN NSs) and fullerene molecules (C60/F) that exhibit multifunctional electrocatalytic properties for the hydrogen evolution/oxidation reactions (HER/HOR) and the oxygen evolution/reduction reactions (OER/ORR). The electrocatalytic properties were studied with varying F:BCN weight ratios to optimize the intermolecular electron transfer (ET) from the BCN NSs to the electron-accepting C60 molecules. The nanohybrid supramolecular material with 10 wt % F in BCN NSs (10% F/BCN) exhibited the largest Raman and C 1s binding energy shifts, which were associated with greater cooperativity interactions and enhanced ET processes at the F/BCN interface. This synergistic interfacial phenomenon resulted in highly active catalytic sites that markedly boosted electrocatalytic activity of the material. The 10% F/BCN showed the highest tetrafunctional catalytic performance, outperforming the OER catalytic activity of commercial RuO2 catalysts with a η10 of 390 mV and very competitive onset potential values of -0.042 and 0.92 V vs RHE for HER and ORR, respectively, and a current density value of 1.47 mA cm-2 at 0.1 V vs RHE with an ultralow ΔGH* value of -0.03 eV toward the HOR process. Additionally, the 10% F/BCN catalyst was also used as both cathode and anode in a water splitting device, delivering a cell potential of 1.61 V to reach a current density of 10 mA cm-2.

Nanoscale nickel metal organic framework decorated over graphene oxide and carbon nanotubes for water remediation.

In this report, highly crystalline and well-dispersed nano-sized nickel metal organic framework (MOFs) was decorated over graphene oxide (GO) and carbon nanotubes (CNTs) platforms to form hybrid nanocomposites. These as-synthesized hybrid nanocomposites were synthesized through a one-pot green solvothermal method. The prepared nanocomposites were characterized by SEM, TEM, EDS, XRD, FT-IR, Raman and TGA techniques. XRD analysis revealed the crystalline structure of the hybrid nanocomposites. Morphological and elemental studies also verified successful decoration of nickel-benzene dicarboxylate (Ni-BDC) MOFs over GO and CNT platforms. Chemical analysis collected through IR, and thermal analysis collected through TGA technique, illustrated the presence of all the components in the hybrid nanomaterials. Methylene blue (MB) was used as a model organic pollutant to analyze the adsorption capacity of the prepared nanocomposites. According to the findings, a strong interaction exists between the MB molecule and the developed adsorbents at which due to the synergistic effect, the hybrid nanocomposites show several times higher adsorption capacity compared to that of parent materials. This improvement can be due to several reasons: high surface area of the MOFs in the composites resulting from the smaller size of MOFs, presence of the pores formed between the MOFs and the platforms and different morphological characteristic of Ni-BDC MOFs in hybrid nanocomposites, compared to bare Ni-BDC MOFs. Furthermore, the isotherm and kinetic studies revealed that the adsorption of MB onto the newly prepared adsorbents could best be explained by the Langmuir and Pseudo-second order kinetic models. A regeneration study demonstrated the highly stable nature of the hybrid nanocomposites.

Sustainable synthesis and remarkable adsorption capacity of MOF/graphene oxide and MOF/CNT based hybrid nanocomposites for the removal of Bisphenol A from water.

A series of novel absorbents based on Cu-BDC MOFs decorated over graphene oxide (GrO) and carbon nanotubes (CNTs) hybrid nanocomposites, namely Cu-BDC@GrO and Cu-BDC@CNT, are synthesized via a facile and one-pot green solvothermal method for water remediation. The nanocomposites were characterized by XRD, TEM, SEM, EDS, Raman, FTIR, TGA, XPS, Zetasizer and ICP-OES instruments. XRD results confirmed the high crystalline structure of the synthesized hybrid nanocomposites. Morphological analysis by SEM and TEM verified the successful decoration of nano-sized Cu-BDC MOFs over GrO and CNT platforms; whereas, EDS and XPS analysis confirmed the presence of all components in the hybrid nanocomposites. Bisphenol A was used in this study as a model organic pollutant that is sometimes present in the industrial wastewater to test the adsorption capacity of the prepared hybrid nanomaterials toward their removal from water. The hybrid nanomaterials showed remarkable adsorption capacity of 182.2 and 164.1 mg/g toward the removal of BPA, which was several times higher than that of 60.2 mg/g for Cu-BDC MOF itself. The Langmuir, Freundlich, Temkin and D-R isotherm models were applied to analyze the experimental data and the results revealed that the Freundlich model describes the experimental data best. A kinetic study was carried out and it showed that the prepared nanomaterials could remove maximum amount of BPA from water in 30 min. The pseudo-first order, pseudo-second order and intra-particle diffusion models were applied to evaluate the kinetic data and the results suggested that the kinetics data could be well fitted to the pseudo-second order kinetic model. Additionally, the BAP adsorption process onto the hybrid nanocomposites was spontaneous and exothermic. The π-π interactions between the BPA and hybrid nanomaterials played a vital role during the BPA adsorption process. The higher adsorption capacity and water stability makes them a good candidate for water remediation applications.