Construction Of Novel Collagen-Based Adsorbent Materials For Dye Adsorption And Oil-Water Separation

Without effective and proper treatment,industrial wastewater containing dyes,heavy metals and oil would lead to environmental problems.Among water treatment technologies,the adsorption method has attracted attention due to its low cost,convenience and high efficiency.The research of adsorption technology focus on the design and construction of absorbent materials.Designing adsorption materials with high specific surface area,porous structure,and abundant adsorption sites is beneficial to improve the adsorption performance.Collagen as a biopolymer in nature,possesses a huge specific surface area and abundant active functional groups,which facilitate its application in adsorption.In this thesis,bovine Achilles tendon was used as raw material to construct collagen-based adsorbents.Collagen aggregates were exfoliated in Na OH/urea solution by freeze-thaw cycles.The collagen aggregates with mesostructure were served as structural units to prepare collagen materials with diversified forms,such as cross-linked collagen sponge（CCS）,tannin/collagen composite fibers（TC）and stearic acid modified collagen sponge（SA-CCS）.Their structure,dyes adsorption properties and oil-water separation performance of collagen-based absorbents were investigated.The main contents are listed below:Cross-linked collagen sponge（CCS）was prepared by glutaraldehyde as a cross-linking agent and mesostructured collagen aggregates as structural units.Scanning electron microscope（SEM）,Fourier transform infrared（FTIR）and thermal analysis（TA）were employed to characterize the structures of CCS.The adsorption capacity of CCS was evaluated by static adsorption experiments by using Congo red（CR）as an anionic dye model.The results of static adsorption experiments indicated that the adsorption behavior of CCS conforms to the Langmuir isotherm model and the pseudo-second-order kinetic model as well as the intraparticle diffusion model.At 333 K,the maximum adsorption capacity(Q_max)of CCS was 232.1 mg/g,which is superior to the reported biomass adsorbents.The results of thermodynamic analysis indicated that the adsorption of CR by CCS could proceed spontaneously.Adsorption-desorption experiments revealed that CCS has excellent stability and reusable ability for removing anionic dyes.Tannin/collagen composite fibers（TC）were successfully prepared by immobilizing black wattle tannins on collagen aggregate carriers with glutaraldehyde as a cross-linking agent.Scanning electron microscope（SEM）,Fourier transform infrared（FTIR）,X-ray photoelectron spectroscopy（XPS）,thermal analysis（TA）and zeta potential were employed to characterize the structures of TC.The adsorption capacity of TC was evaluated by static adsorption and dynamic continuous fixed-bed adsorption experiments using methylene blue（MB）as the cationic dye model.Results of static adsorption experiment indicated that the adsorption behaviors of TC conformed to the Freundlich isotherm model and the pseudo-second-order kinetic model as well as the intraparticle diffusion model.The maximum adsorption amount(Q_max)of TC was 46.5 mg/g at 303 K.The results of thermodynamic analysis indicated that the adsorption of MB by TC could proceed spontaneously.Fixed-bed adsorption experiments revealed that the initial concentration,flow rate,and column height significantly influenced the removal of MB,and all breakthrough curves were well fitted by Thomas and Yoon-Nelson models.Adsorption-desorption experiments demonstrated that TC possessed excellent stability and reusable ability for cationic dye.The collagen sponges with a connected porous structure were prepared by collagen aggregates as the basic structural unit,and their hydrophobicity was improved by introducing stearic acid modified collagen sponge（SA-CCS）with a connected porous structure.Scanning electron microscope（SEM）and Fourier transform infrared（FTIR）were employed to characterize the structures of SA-CCS.The results showed that stearic acid crystallized on the porous collagen sponge skeleton to form a rough and hydrophobic structure,endowing the sponge with good hydrophobicity and adsorption abilities for oily organic reagents.The performance test results demonstrated that the composite sponge adsorbed the oil phase up to 10-23 times its own weight.The cyclic oil adsorption experiment indicated that the sponge still had stable and repeatable oil adsorption ability.In addition,the prepared composite sponge also had the ability to continuously separate oil-water mixtures and water-in-oil emulsions.Multiple cycles of oil-water separation experiments demonstrated that the sponge still had good flux and separation efficiency.