Study On Separation Of Main Components From Corncob Residues And Their High-value Utilization

Lignocellulosic biomass is regarded as an ideal renewable resource for replacing traditional fossil fuels.Corncob residues(CRs)generated after hemicelluloses pre-extraction of corncobs were considered to be potential feedstocks to produce bio-based products such as cellulose nanopaper(CNP),lignin-based products,and carbon quantum dots(CQDs).Firstly,a strong and optically transparent nanopaper was fabricated from cellulose nanofibril(CNF)of corncob residues.Two processes were applied to generate cellulose nanofibril(CNF)and cellulose nanopaper(CNP)from CRs.The resultant CNF mainly consists of fibers with diameter(height)of about 1.0-5.0 nm on average.The as-prepared CNP exhibited good strength,optical,and thermal properties.Compared with B-CNP,A-CNP showed much higher optical properties and hydrophobicity,similar thermal ability,but slightly lower strength properties,i.e.,the tensile strength and tensile fracture strain of A-CNP was 65.3 MPa and 2.3%,respectively;the optical transmittance was close to 90%in the visible range;the highest degradation peak temperature was about 290?:the water contact angle at 30 s was 68.2°.The results showed that the CNP has some potential applications in flexible electronic products and energy products.Secondly,three lignin fractions,i.e.,dioxane lignin(DL),milled-wood lignin(MWL),and enzymatic mild acidolysis lignin(EMAL),were isolated from CRs,and characterized by HPLC,GPC,FT-IR,NMR,and TGA to reveal characteristics of CRs lignin.The results showed that the yield of DL,MWL and EMAL were 12.8%,14.7%and 15.6%,respectively;the molecular weight of DL,MWL and EMAL were 2001,5391,and 2629 g/moL,respectively;the EMAL and MWL had similar structural features including guaiacyl and syringyl units,?-O-4' aryl ether,p-coumaric acids,ferulates,and phenylcoumarans,while the structure of DL was relatively simple.Finally,the nitrogen-doped CQDs(N-CQDs)were synthesized using a simple,green,energy-saving,and efficient hydrothermal method from CRs and the enzymatically hydrolyzed corncob residues(EHCRs).The two kind of resultant CQDs were characterized and their applications in detection of metal ions were investigated.The results showed that CRs and EHCRs were good sources for CQDs;the nitrogen doping improved the fluorescence intensity and stability of CQDs;the nitrogen-doped CQDs from EHCRs(E-N-CQDs)exhibited the strongest fluorescence compared with other CQDs;the E-N-CQDs had a strong emission at a wavelength of 414 nm and an optimal excitation wavelength of 318 nm.the strongest fluorescence intensity was found at pH 10.0;the E-N-CQDs were the most sensitive to Fe(?)with the detection limit of 0.75 ?mol/L.which was much lower than the concentration of Fe(?)in human blood(7.52-11.82 mmol/L).Then the developed E-N-CQDs concept may provide a novel method for the detection of Fe(?)in human blood.