Preparation And Performance Of Carboxyl Carbon Quantum Dot Scale Inhibitor

In recent years,along with our country population growth and the degree of industrialization modernization deepening,the demand for water increased further,water resource is very scarce.In industrial production,water consumption is huge.In order to make better use of water resources,cooling water must be recycled.However,as the number of cycles increases,the concentration of metal ions in the water increases,leading to severe scaling and corrosion of metal pipes,resulting in serious damage to the heat transfer system.The damage of the heat transfer system will reduce the heat transfer efficiency,greatly reduce the service time of the pipeline equipment,significantly increase the heat and electric energy consumption,and increase the maintenance cost of the equipment.Adding scale inhibitors is the most convenient and effective method to solve the scaling problem.Therefore,it is of great significance to develop new environmental protection scale inhibitor,and the economic benefits are more direct.Firstly,using citric acid and L-ascorbic acid as raw materials,L-CCQDs carbon quantum dot scale inhibitor was synthesized by a pot of hot melt polycondensation method.According to the national standard GB/T16632-2008 and SY/T5673-93,the scale inhibitor L-CCQDs were tested,and the preparation conditions of L-CCQDs were optimized by measuring different synthesis times,synthesis temperatures and raw material ratios,and the optimal synthesis conditions for L-CCQDs were determined to have a molar mass ratio of anhydrous citric acid to L-ascorbic acid of2:1,a reaction temperature of 200 °C,and a reaction time of 1 hour.Transmission electron microscopy(TEM)shows that L-CCQDs are spherical and have particle sizes between 2 nm and 3 nm.Fourier infrared spectroscopy(FTIR)confirmed that the surface of carbon quantum dots contains carboxyl groups and a small amount of ester functional groups.Ultraviolet absorption spectroscopy(UV-Vis)indicates that the molecular structure contains non-conjugated double bonds.The scale inhibition rate of L-CCQDs on calcium carbonate and calcium sulfate scale under different water conditions was evaluated.Finally,SEM and XRD were used to study the lattice and morphology of calcium carbonate and calcium sulfate scale,and the possible scale inhibition mechanism of L-CCQDs was analyzed.It was found that the carboxyl carbon quantum dots(CCQDs)synthesized by thermal decomposition of pure citric acid could have a maximum scale inhibition effect of 95 % on calcium sulfate scale when the synthesis temperature was 80 °C,the synthesis time was 30 h,and the additive content was 25 mg/L.The scale inhibition rate of L-CCQDs against calcium carbonate scale at a dose of 50 mg/L is 97 %,and the scale inhibition rate of calcium sulfate scale at a dose of 10 mg/L can reach 98 %,so the scale inhibitors L-CCQDs synthesized in this experiment can achieve better scale inhibition effect than CCQDs at fewer doses.In order to further improve the scale inhibition performance of L-CCQDs,a carbon quantum dot scale inhibitor Ly-CCQDs was synthesized using L-lysine and anhydrous citric acid as raw materials in the same way.The preparation conditions of Ly-CCQDs were optimized by measuring different synthesis time,synthesis temperature and raw material ratio.The optimum synthesis conditions were determined as the molar mass ratio of anhydrous citric acid to L-lysine was 5:1,the reaction temperature was 200 °C and the reaction time was 1.5 hours.The diameter of Ly-CCQDs was observed by transmission electron microscopy in the range of 4 nm-5nm.Fourier infrared spectroscopy confirmed that the surface of carbon quantum dots contains a large number of carboxyl groups,and the structure contains a large number of amino groups.Ultraviolet absorption spectra can confirm that the molecular structure contains non-phase conjugated double bonds.The scale inhibition rate of Ly-CCQDs on calcium carbonate and calcium sulfate was evaluated under different water conditions.The scale inhibition effect of L-CCQDs and Ly-CCQDs in long time high temperature water was compared.Finally,the lattices and morphologies of calcium carbonate scale and calcium sulfate scale were studied by SEM and XRD,and the scale inhibition mechanism of Ly-CCQDs was discussed.The experimental results show that the modified Ly-CCQDs has better scale inhibition effect than L-CCQDs.The scale inhibition rate of Ly-CCQDs on calcium carbonate is 98 % at the dosage of 20 mg/L,and the scale inhibition rate of calcium sulfate is up to 99 % at the dosage of 5 mg/L,and the scale inhibition effect of Ly-CCQDs is better than that of L-CCQDs in the water that maintains high temperature for a long time.Similar to L-CCQDs,the inhibition process of calcium carbonate scale formation is mainly chelation and dispersion,while the inhibition process of calcium sulfate scale formation is mainly chelation,dispersion and lattice distortion,and the lattice distortion mechanism contains a certain degree of threshold effect.