Corrosion Control Of Sulfate-reducing Bacteria By Nitrogen-doped Carbon Quantum Dots

As industrialization process is accelerated,the usage amount of carbon steel increases year by year,at the same time,the economic losses resulted from carbon steel corrosion also increases year by year.Microbiologically influenced corrosion is a common type of corrosion for industrial system,especially the oil industrial system,and serious accidents caused by microbiologically influenced corrosion of pipeline,equipment,etc.occur every year.Now,chemical germicides such as glutaric dialdehyde and tetrakis hydroxymethyl phosphonium sulfate（THPS）are usually added to the pipeline to inhibit microbiologically influenced corrosion,besides,some scholars suggest that microbiologically influenced corrosion can also be inhibited through competition between less corrosive microbes such as nitrate reducing bacteria and corrosive microbes for living space and carbon source.The germicides frequently used in the industry are usually toxic and will damage the environment,while it is difficult to control the behavior of microbes when inhibiting with microbes,so a non-toxic,green and efficient microbial corrosion inhibitor is needed.Carbon quantum dots are a new carbon-based material.A lot of reports indicate that carbon quantum dots have broad-spectrum antibacterial activity and show good antibacterial effect for both gram-negative bacteria and gram-positive bacteria.This paper takes trisodium citrate and straw as the carbon source and carbamide as the nitrogen source to synthesize N-doped carbon quantum dots,compares the method of using N-doped carbon quantum dots to inhibit the corrosion of sulfate reducing bacteria dominating the corrosive microbes for carbon steel with the methods of microbial inhibition and conventional chemical inhibition,and explores the feasibility of using N-doped carbon quantum dots to inhibit microbiologically influenced corrosion.The results are as follows:（1）After co-culture of nitrate reducing bacteria and sulfate reducing bacteria,the uniform corrosion rate of Desulfovibrio desulfuricans（SRB₁）decreases from 0.288 mm/y to 0.130 mm/y,and the 7-day average pitting corrosion depth decreases from 18.053μm to 8.799μm;The uniform corrosion rate of Desulfovibrio vulgaris（SRB₂）decreases from0.344 mm/y to 0.138 mm/y,and the average pitting corrosion depth decreases from19.607μm to 7.711μm.（2）After use of glutaric dialdehyde and THPS as germicides,the uniform corrosion rates of SRB₁ are 0.172 mm/y and 0.167 mm/y respectively,and the pitting corrosion depths decrease to 8.002μm and 8.424μm respectively;The uniform corrosion rates of SRB₂ are 0.176 mm/y and 0.161 mm/y respectively,and the average pitting corrosion depths are 8.226μm and 8.180μm respectively.The inhibition effect is less satisfactory than NRB.The inhibition effects of two ionic liquids of 1-Butyl-3-methylimidazolium tetrafluoroborate and 1-Butylpyridinium chloride are better.After addition of germicides,the uniform corrosion rates of SRB₁ are 0.125 mm/y and 0.140 mm/y respectively,and the average pitting corrosion depths are 7.926μm and 7.233μm respectively;the uniform corrosion rates of SRB₂ are 0.157 mm/y and 0.155 mm/y respectively,and the average pitting corrosion depths are 7.701μm and 7.433μm.The two ionic liquids have similar inhibition effect with NRB and even show better inhibition effect for pitting corrosion than NRB.（3）N-CQDs synthesized with trisodium citrate as carbon source show antibacterial activity for both two SRB bacteria.After addition of 0.5-2.0 mg/m L N-CQDs,the uniform corrosion rate of SRB₁ is 0.113-0.190 mm/y,and the average pitting corrosion depth is8.643-9.847μm;the uniform corrosion rate of SRB₂ is 0.156-0.186 mm/y,and the average pitting corrosion depth is 7.505-10.979μm.The inhibition effect is superior to glutaric dialdehyde and THPS frequently used in the industry,and the inhibiting ability for uniform corrosion is better than two ionic liquids and close to NRB;the pitting corrosion inhibition effect for SRB₂ is close to two ionic liquids and NRB,but the pitting corrosion inhibition effect for SRB₁ is not so good.（4）After use of N-SCQDs prepared with straw as carbon source as germicide,when the amount of addition is 1.0 mg/m L,the inhibition effect for SRB₁ is the best,now the uniform corrosion rate of SRB₁ is 0.141 mm/y,and the average pitting corrosion depth is7.937μm;The best amount of addition for SRB₂ is 1.5 mg/m L,now the uniform corrosion rate is 0.120 mm/y,and the average pitting corrosion depth is 7.769μm.The inhibition effect is superior to glutaric dialdehyde and THPS,close to imidazole ionic liquid and NRB and poorer than pyridine ionic liquid.In conclusion,carbon quantum dots show bacteriostatic activity for sulfate reducing bacteria dominating the corrosive microbes and have the potential of becoming an efficient,green microbiologically influenced corrosion inhibitor.