Preparation Of Micro/Nano-scaled Copper Phosphates And Research Of Their Photothermal Properties

Photothermal materials are those that can absorb photon energy of a specific light and then convert it into heat.At present most photothermal materials are used as photothermal agents for light-to-heat converting of solar energy and photothermal therapy（PTT）of tumors.Visible and infrared light energy respectively accounts for 50% and 43% of the total solar energy that reaches the ground.Moreover visible and and near-infrared（vis-NIR）light has deeper penetration in biological tissues than ultraviolet（UV）light and can kill cancer cells in deep tissues more efficiently than UV light.As a result,vis-NIR light absorbing materials are attracting more attention of scientists.In this thesis,a novel photothermal material of copper phosphates（CuPOs）was well designed and fabricated based on d-d transition of 3d electrons in Cu²⁺.A very strong vis-NIR absorption within 400-1200 nm band was observed for the prepared CuPOs,which could further generate heat highly efficiently.The light-to-heat converting efficiency of the prepared CuPOs was measured and the light-to-heat converting mechanism was investigated in details.We also explored the applications of CuPOs as photothermal agents in solar evaporation of salt water and photothermal therapy of tumors.The main contents of this thesis are listed as follows:1.Study on fabrication,photothermal properties and light-to-heat mechanism of the novel CuPOs photothermal materials.（1）Micro/nano-scaled CuPOs with three different morphologies were synthesized via hydrothermal and solvothermal method.They were sheet-like CuPOs with sheet thickness of about 2 nm,flower-like CuPOs with diameter of about 3-5 μm and hierarchical structure assembled by nanosheets,and sphere-like CuPOs with a particle size of 140-160 nm.（2）Photothermal properties of the prepared CuPOs were investigated by using a 808 nm NIR laser.The photothermal conversion efficiency（?1）was calculated to be 30.85%,41.8% and 34.6%,respectively,for the three different CuPOs.Microstructural morphology was found to influence on photothermal properties of CuPOs,in which flower-like CuPOs exhibited the most favorable photothermal properties since the photoabsorption could be remarkably enhanced due to multiple reflection of light among the CuPOs flower petals.（3）With the UV-vis-NIR diffuse reflectance data,the Eg value of the prepared CuPOs was calculated.The mechanism of light-to-heat behavior of CuPOs was proposed based on d-d transition of 3d electrons in Cu²⁺.2.Study on applications of the photothermal CuPOs in solar evaporation of seawater.（1）Floating photothermal sheets were fabricated by compositing the flower-like CuPOs,which has the highest ?1 value under the irradiation of 808 nm laser,with intrinsically hydrophobic polydimethylsiloxane（PDMS）.The hydrophobicity of the prepared CuPOs-PDMS photothermal sheets was further improved with the assistance of rough surface of sandpapers,in which an apparent contact angle of 124.0o was obtained.Due to the self-floating capability of CuPOs-PDMS sheets,the heat generated by CuPOs was well confined within water-air interface region,which greatly accelerated solar evaporation of seawater.（2）The performances of the CuPOs-PDMS photothermal sheets in water evaporation were characterized by using a solar simulator as a light source and NaCl aqueous solution containing 3.5 wt% NaCl as simulated seawater.Experimental results demonstrated that water evaporation rate of salt water was measured to be 1.01 kg·m-2·h-1 for porous floating CuPOs-PDMS sheets（40 wt% CuPOs）under a power density of 1000 W·m-2.A very high solar thermal conversion efficiency of 63.6% was obtained,which was 1.71 times of that measured for ordinary salt water,indicating that solar evaporation of salt water could be greatly enhanced by the prepared CuPOs-PDMS sheets.3.Study on applications of the photothermal CuPOs as a PTT agent for tumors.Sphere-like CuPOs with a endocytosis favorable size was used to investigate the applications of photothermal CuPOs as a PTT agent for tumors.Human cervical cancer cell（HeLa cell）line was used as a cell model.PTT effect was evaluated by incubating HeLa cells merely with CuPOs nanospheres(125 μg·mL^-1)for 2 h,and then irradiated by 808 nm laser light for 5 min.The cell viability decreased from 86.9% before PTT to 77% and 40%,respectively,after PTT was carried out by with a laser power density of 0.1 W·cm-2 and 0.3 W·cm-2.4.Study on peroxidase mimetic activities of the prepared micro/nano-scaled CuPOs.We found that our CuPOs had catalytic activities similar to natural peroxidase besides excellent photothermal properties.（1）The redox reaction between TMB and H₂O₂ was carried out to study the peroxidase mimetic activity of the prepared CuPOs.In solution,colorless TMB forms a blue product when allowed to react with peroxidase enzymes.This reaction was found to be catalyzed by our CuPOs just like natual peroxidase,indicating the peroxidase mimetic activities of CuPOs.The catalytic activity of the CuPOs was found to dependent on pH.For sphere-like CuPOs a pH value of 3.2 was the optimal pH for its peroxidase-like activities.（2）Taking advantage of the peroxidase-like activities of CuPOs,water soluble conductive polythiophene（PEDOT）was synthesized by using CuPOs as a catalyst just as natural peroxidase do.（3）The mechanism of the peroxidase-like activities of CuPOs was investigated by lumino chemiluminescence reaction.Experimental results of CuPOs-catalyzed lumino chemiluminescence reaction demonstrated the ability of CuPOs to catalyze H₂O₂ decomposition into ·OH radicals,since CuPOs-catalyzed lumino chemiluminescence only only operated in the presence of H₂O₂.（4）Based on their peroxidase-like activities,the applications of CuPOs nanospheres were further investigated in reactive oxygen species（ROS）activated tumor therapy.Cell viability of HeLa cells co-cultured merely with CuPOs nanospheres(125 μg·m L^-1)for 2 h was 86.9%,but decreased to only 49.8% after further co-cultured with subsequently added H₂O₂（1.25 mM）,indicating that interalized CuPOs nanospheres could kill cancer cells by decomposing H₂O₂ into harmful ·OH radicals.Tumor killing efficiency could be further improved by synergistic effect of combined PTT and ROS activated therapy of CuPOs.