This review is a summary of the Raman spectroscopy applications made over the last 10 years in the field of cellulose and lignocellulose materials. This paper functions as a status report on the ...kinds of information that can be generated by applying Raman spectroscopy. The information in the review is taken from the published papers and author's own research-most of which is in print. Although, at the molecular level, focus of the investigations has been on cellulose and lignin, hemicelluloses have also received some attention. The progress over the last decade in applying Raman spectroscopy is a direct consequence of the technical advances in the field of Raman spectroscopy, in particular, the application of new Raman techniques (e.g., Raman imaging and coherent anti-Stokes Raman or CARS), novel ways of spectral analysis, and quantum chemical calculations. On the basis of this analysis, it is clear that Raman spectroscopy continues to play an important role in the field of cellulose and lignocellulose research across a wide range of areas and applications, and thereby provides useful information at the molecular level.
The photoelectrochemical (PEC) cell that collects and stores abundant sunlight to hydrogen fuel promises a clean and renewable pathway for future energy needs and challenges. Monoclinic bismuth ...vanadate (BiVO4), having an earth‐abundancy, nontoxicity, suitable optical absorption, and an ideal n‐type band position, has been in the limelight for decades. BiVO4 is a potential photoanode candidate due to its favorable outstanding features like moderate bandgap, visible light activity, better chemical stability, and cost‐effective synthesis methods. However, BiVO4 suffers from rapid recombination of photogenerated charge carriers that have impeded further improvements of its PEC performances and stability. This review presents a close look at the emerging surface, bulk, and interface engineering strategies on BiVO4 photoanode. First, an effective approach of surface functionalization via different cocatalysts to improve the surface kinetics of BiVO4 is discussed. Second, state‐of‐the‐art methodologies such as nanostructuring, defect engineering, and doping to further enhance light absorption and photogenerated charge transport in bulk BiVO4 are reviewed. Third, interface engineering via heterostructuring to improve charge separation is introduced. Lastly, perspectives on the foremost challenges and some motivating outlooks to encourage the future research progress in this emerging frontier are offered.
In this review, recent progress in emerging surface, bulk, and interface engineering strategies to improve the photoelectrochemical (PEC) performance of bismuth vanadate (BiVO4) photoanode is systemically elaborated. Discussed strategies offer an in‐depth understanding of the relationship between engineered BiVO4 photoanode and its PEC performance. Forward‐looking perspectives on the current challenges and future opportunities of the BiVO4 photoanode frontier are also provided.
Cellulose nanocrystals (CNC) have recently received much attention in the global scientific community for their unique mechanical and optical properties. Here, we conducted the first detailed ...exploration of the basic properties of CNC, such as morphology, crystallinity, degree of sulfation and yield, as a function of production condition variables. The rapid cellulose depolymerization and sulfation reactions under concentrated acid concentrations of around 60 wt% resulted in a very narrow operating window for CNC production. We found that CNC yields as high as 70 wt% from a bleached eucalyptus kraft pulp with glucan content of 78 wt% can be achieved under a tight range of reaction conditions and that a weighted average length of over 200 nm and sulfur content (a measure of CNC surface charge) between 3 and 10 mg/g can be produced. This study provided critical knowledge for the production of CNC with characteristics tailored for different specific applications, significant to commercialization.
Raman spectroscopy with its various special techniques and methods has been applied to study plant biomass for about 30 years. Such investigations have been performed at both macro- and micro-levels. ...However, with the availability of the Near Infrared (NIR) (1064 nm) Fourier Transform (FT)-Raman instruments where, in most materials, successful fluorescence suppression can be achieved, the utility of the Raman investigations has increased significantly. Moreover, the development of several new capabilities such as estimation of cellulose-crystallinity, ability to analyze changes in cellulose conformation at the local and molecular level, and examination of water-cellulose interactions have made this technique essential for research in the field of plant science. The FT-Raman method has also been applied to research studies in the arenas of biofuels and nanocelluloses. Moreover, the ability to investigate plant lignins has been further refined with the availability of near-IR Raman. In this paper, we present 1064-nm FT-Raman spectroscopy methodology to investigate various compositional and structural properties of plant material. It is hoped that the described studies will motivate the research community in the plant biomass field to adapt this technique to investigate their specific research needs.
•Cellulose nanocrystal was modified by canola oil fatty acid methyl ester (CME).•CME performs as both the reaction reagent and solvent.•Hydrophobic long chain hydrocarbons (C16 and C18) were grafted ...onto CNC surfaces.•Sizes of transesterified CNCs were smaller than unmodified CNCs.•3-D crystalline structure of CNCs was not altered by modification.
Cellulose nanocrystals (CNCs), produced from dissolving wood pulp, were chemically functionalized by transesterification with canola oil fatty acid methyl ester (CME). CME performs as both the reaction reagent and solvent. Transesterified CNC (CNCFE) was characterized for their chemical structure, morphology, crystalline structure, thermal stability, and hydrophobicity. Analysis by Fourier transform infrared (FTIR) and FT-Raman spectroscopies showed that the long chain hydrocarbon structure was successfully grafted onto CNC surfaces. After transesterification the crystal size and crystallinity of nanocrystals were not changed as determined by Raman spectroscopy and wide angle X-ray diffraction (XRD). CNCFE showed higher thermal stability and smaller particle size than unmodified CNCs. Water contact angle measurement indicated the CNCFE surface has significantly higher hydrophobicity than unmodified CNCs. The transesterified CNCs could be potentially used as hydrophobic coatings and reinforcing agents to hydrophobic polymer for nanocomposites.
Although X-ray diffraction (XRD) has been the most widely used technique to investigate crystallinity index (CrI) and crystallite size (L
200
) of cellulose materials, there are not many studies that ...have taken into account the role of sample moisture on these measurements. The present investigation focuses on a variety of celluloses and cellulose containing materials—from loblolly pine wood to tunicin, and evaluated moisture-induced changes in CrI and L
200
. It was observed that upon introduction of a small amount of water (5%) into P
2
O
5
dried samples, for most samples, both absolute intensity of (200) reflection and its full width at half maximum declined. Moreover, (200) peak position (2θ max) increased when the samples became moist. Although the extent of such changes were material dependent, in general, a greater degree of change was associated with lower sample CrI. For CrI, maximum and minimum increases occurred for oven dried NaOH treated red pine holopulp and tunicin, respectively. For L
200
, maximum and minimum increases were for wood and tunicin, respectively. Moreover, 2θ max position for (200) reflection increased most for the wood and oven dried NaOH treated red pine holopulp (acid chlorite delignified milled-wood) and least for tunicin. The nonparametric statistical test “sign test” further supported these results. Observations from longer duration drying experiments, post moistening, indicated that the changes to the XRD parameters were reversible to some degree. Based on the findings it is concluded that for most cellulose materials with Segal CrI < 90% the moisture content has a significant bearing on the XRD-estimated CrI and L
200
data. Consequently, it is essential that when such materials are compared, their diffractograms should be obtained under similar levels of sample moisture content.
A detailed understanding of the structural organization of the cell wall of vascular plants is important from both the perspectives of plant biology and chemistry and of commercial utilization. A ...state-of-the-art 633-nm laser-based confocal Raman microscope was used to determine the distribution of cell wall components in the cross section of black spruce wood in situ. Chemical information from morphologically distinct cell wall regions was obtained and Raman images of lignin and cellulose spatial distribution were generated. While cell corner (CC) lignin concentration was the highest on average, lignin concentration in compound middle lamella (CmL) was not significantly different from that in secondary wall (S2 and S2-S3). Images generated using the 1,650 cm-1 band showed that coniferaldehyde and coniferyl alcohol distribution followed that of lignin and no particular cell wall layer/region was therefore enriched in the ethylenic residue. In contrast, cellulose distribution showed the opposite pattern--low concentration in CC and CmL and high in S2 regions. Nevertheless, cellulose concentration varied significantly in some areas, and concentrations of both lignin and cellulose were high in other areas. Though intensity maps of lignin and cellulose distributions are currently interpreted solely in terms of concentration differences, the effect of orientation needs to be carefully considered to reveal the organization of the wood cell wall.
Conversion of lignocellulose to biofuels is partly inefficient due to the deleterious impact of cellulose crystallinity on enzymatic saccharification. We demonstrate how the synergistic activity of ...cellulases was enhanced by altering the hydrogen bond network within crystalline cellulose fibrils. We provide a molecular-scale explanation of these phenomena through molecular dynamics (MD) simulations and enzymatic assays. Ammonia transformed the naturally occurring crystalline allomorph Iβ to IIII, which led to a decrease in the number of cellulose intrasheet hydrogen bonds and an increase in the number of intersheet hydrogen bonds. This rearrangement of the hydrogen bond network within cellulose IIII, which increased the number of solvent-exposed glucan chain hydrogen bonds with water by ∼50%, was accompanied by enhanced saccharification rates by up to 5-fold (closest to amorphous cellulose) and 60–70% lower maximum surface-bound cellulase capacity. The enhancement in apparent cellulase activity was attributed to the “amorphous-like” nature of the cellulose IIII fibril surface that facilitated easier glucan chain extraction. Unrestricted substrate accessibility to active-site clefts of certain endocellulase families further accelerated deconstruction of cellulose IIII. Structural and dynamical features of cellulose IIII, revealed by MD simulations, gave additional insights into the role of cellulose crystal structure on fibril surface hydration that influences interfacial enzyme binding. Subtle alterations within the cellulose hydrogen bond network provide an attractive way to enhance its deconstruction and offer unique insight into the nature of cellulose recalcitrance. This approach can lead to unconventional pathways for development of novel pretreatments and engineered cellulases for cost-effective biofuels production.
High lignin-containing cellulose nanocrystals (HLCNCs) were successfully isolated from hydrothermally treated aspen fibers and freeze-dried and compounded with poly (lactic acid) (PLA) by extrusion ...and injection molding. As a comparison, PLA composites containing commercial lignin-coated CNCs (BLCNCs) were also produced. HLCNCs showed higher crystallinity, larger surface area, lower degree of agglomeration, and more hydrophobic surfaces compared to BLCNCs, as characterized by electron microscopy, surface area measurements, thermal analysis, spectroscopy and water contact angle measurements. The effect of lignin and CNC morphology on the mechanical, thermal and viscoelastic properties and CNCs/polymer interfacial adhesion of nanocomposites was investigated with tensile test, DSC and DMA. Compared to neat PLA, the Young's modulus, elongation to break, and toughness of PLA/2%HLCNCs were improved by 14, 77, and 30%, respectively. HLCNCs and BLCNCs act as nucleating fillers, increasing the degree of crystallinity (χc) of PLA in nanocomposites. The presence of lignin nanoparticles in the HLCNC increased the compatibility/adhesion between CNCs and polymer matrix which increased the storage modulus.
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•High-lignin-containing CNCs (HLCNCs) were used as nanofiller for PLA matrix.•HLCNC has lower agglomeration degree and higher hydrophobicity and surface area.•Lignin nanoparticles increased the compatibility of filler and polymer matrix.•HLCNCs based nanocomposites showed higher degree of crystallinity than neat PLA.•Adding HLCNCs increased the viscoelastic properties as compared to neat PLA.
Here, a hierarchical nanostructure composed of Ni-doped α-FeOOH (Ni:FeOOH) nanosheets coupled with N-doped graphite foam (NGF) is demonstrated as a three-dimensional (3D) self-supported ...electrocatalyst for highly efficient and durable water oxidation. A facile, one-step directional growth of catalytically active Ni:FeOOH nanosheets on highly conducting 3D NGF results in a fully integrated, hierarchical, nanostructured electrocatalyst with (i) the high intrinsic activity of Ni:FeOOH, (ii) the outstanding electrical conductivity of NGF, and (iii) a well-defined porous structure with an enhanced active surface area. As a result, the self-supported 3D Ni:FeOOH/NGF electrocatalyst exhibits remarkable electrocatalytic activity for the oxygen evolution reaction (OER) in an alkaline solution with an overpotential of 214 mV at 10 mA/cm2, a high stability for over 60 h, a low Tafel slope of 36.2 mV dec–1, and a capability of delivering a high current density of 300 mA/cm2 at an overpotential of 368 mV. In contrast to photodeposition, electrodeposition, and hydrothermal methods for the formation/integration of (oxy)hydroxides, this facile solution strategy for designing an attractive and efficient structure with a highly active metal (oxy)hydroxide and highly conducting NGF provides a pathway to develop other earth-abundant electrocatalysts for a multitude of energy-conversion-device applications.
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