| With the development of nanotechnology and higher requirement for environment protection,nanofibrillated cellulose (NFC) derived from plants has caught widely attention of scientists andtechnologists. NFC can be used as the natural template since it has high specific surface area,abundant hydroxyl, and microporous structure. This template effect is enhanced by modifying theNFC with carboxyl. NFC has good film-forming property, high membrane elastic modulus, andhigh transparency. Taking NFC as the template for synthesizing inorganic semiconductornanoparticles, a new kind of nanocomposite material with excellent optical, mechanical, andelectrical properties can be expected and can be applied in light electric transformation domain.TEMPO/NaClO/NaBr oxidation system was applied to treat eucalyptus wood pulp andoxidized celluloses with different carboxylate content were prepared by changing the dosage ofNaClO. Combined with high pressure homogeneous processing, a series of nanofibrillatedcelluloses (NFCs) with different carboxylate content were obtained and their crystalline structureand morphology structure were characterized by XRD and TEM. The saturated adsorptionamount of Cd2+to NFC was determined by atomic absorption spectroscopy. NFC/CdSnanocomposites with CdS nanoparticles quantum dots were controllably prepared by controllingthe molar ratio of COO-/Cd2+via an in-situ process. The structure of NFC/CdS nanocompositeswas investigated by FTIR, XRD, and TEM. NFC/CdS nanocomposite film was obtained byvacuum filtration method, for the usage of photoelectric conversion device. The optical,mechanical, and electrical properties of the film were characterized. The results were showed asfollows.1. When eucalyptus wood pulp was oxidized by TEMPO/NaClO/NaBr oxidation systemwith dosage of NaClO of6,8,10,12mmol/g respectively, TEMPO oxidized celluloses withcarboxylate content of0.71,0.92,1.17,1.23mmol/g were obtained.2. NFC was obtained by treating the above TEMPO oxidized celluloses with high pressurehomogeneous processing. The NFCs’ width were in the range of9~30nm,8~28nm,5~20nm,4~18nm respectively.3. The saturated adsorption amount of Cd2+to NFC was determined by atomic absorption spectrometry. The relationship between the NFC’s carboxylate content and the saturatedadsorption amount of Cd2+was as following: COO-/Cd2+(molar ratio)≈2:1.4. Using the above NFCs as templates, the NFC/CdS nanocomposites were obtained byin-situ process and controlling the molar ratio of COO-/Cd2+as2:1. FITR showed a stronginteraction between NFC’s carboxylate and CdS. XRD showed that the CdS nanoparticles werecubic crystal structure, and the average sizes were9.62nm,17.59nm,13.50nm,12.9nmrespectively. TEM showed that CdS particles were uniformly distributed on the surface of NFC.CdS nanoparticles quantum dots were observed and their average particle sizes were6.75nm,10.2nm,6.05nm,7.85nm.5. By controlling the molar ratio of COO-/Cd2+as1:1, NFC/CdS nanocomposites wereobtained with matrix’s carboxylate contents0.92mmol/g and1.23mmol/g. The NFC/CdSnanocomposites were compared with those prepared at the molar ratio of COO-/Cd2+as2:1. XRDshowed that compared with those prepared at the molar ratio of COO-/Cd2+as2:1, sizes of CdSparticles of NFC/CdS nanocomposites prepared at the molar ratio of COO-/Cd2+as1:1decreasedfrom17.59nm,12.9nm to11.93nm,11.5nm respectively. TEM showed the average sizesdecreased from10.2nm,7.9nm to5nm,6.6nm, but CdS particles agglomerated in local places.From the results above, by controlling the molar ratio of COO-/Cd2+as2:1, it was much easier torealize uniform distribution of CdS nanoparticles and controllable preparation of NFC/CdSnanocomposites with CdS nanoparticles quantum dots.6. NFC/CdS nanocomposites prepared at the molar ratio of COO-/Cd2+as2:1was used tofabricate composites films and the films’properties were tested. Results showed that the moduluselastic of NFC/CdS nanocomposite film was higher than that of NFC film and increased with theincreasing of NFC’s carboxylate content. When the carboxylate content of NFC was1.23mmolg/g, the modulus elastic of NFC/CdS nanocomposite film reached up to8.1Gpa, whichwas3times of the matrix NFC film. The transmittance of NFC/CdS nanocomposite film wasincreased with the increasing of matrix’s carboxylate content and could be as high as97.12%.The photocurrents of NFC/CdS nanocomposites were0.71A,1.20A,1.72A,1.98μArespectively, which increased with the increasing of NFC’s carboxylate content and showed goodstability. The relationship between photocurrent(Y) and carboxylate content(X) could beapproximately described as following: Y=2.3468X-0.9619 7. In order to reveal the effect the molar ratio of COO-/Cd2+on the nanocomposite film’sproperties, NFC/CdS nanocomposites prepared at the molar ratio of COO-/Cd2+as1:1whichmatrixs’ carboxylate contents were0.92mmol/g,1.23mmol/g were also used to fabricatenanocomposites films. Results showed that compared with those which was obtained at the molarratio of COO-/Cd2+as2:1, nanocomposite films prepared at the molar ratio of COO-/Cd2+as1:1had lower modulus elastic, which decreased from7.4GPa,8.1GPa to6.0GPa,7.1GParespectively; their transmittance represented irregular change, the former increased from76.74%to96.43%, while the latter decreased from90.50%to89.79%; their photocurrents increased from1.20A,1.98A to2.10A,2.12A respectively, which was also irregular. In summary,NFC/CdS nanocomposites films with better optical, mechanical, and opto-electrical propertiescould be obtained by controlling the molar ratio of COO-/Cd2+as2:1to prepare NFC/CdSnanocomposites. |
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