Photodegradation Kinetics and Mechanism of Bisphenol-A and 4-tert-octylphenol in Aqueous Solution

학위논문 (석사)-- 서울대학교 보건대학원 : 환경보건학과, 2012. 8. 조경덕.내분비장애물질(endocrine disrupting compounds)로 알려진 비스페놀-A와 4-tert-옥틸페놀은 기존 하∙폐수처리장에 분해효율이 낮고, 인체에 들어와 유방암, 경련, 그리고 고환암 등의 건강영향을 일으키기 때문에 시급한 처리가 필요하다. 광분해는 적절히 적용된다면기존 처리방법과 달리 오염물을 완전히 무기화(mineralization) 시킬수 있기 때문에 내분비계장애물질처리에 가장 적합한 처리 방법이다. 하지만 분해에 영향을 미치는 인지와 분해중간체(intermediate)를 재대로 파악하지 않고처리 공정에 도입하면설계, 비용, 운전측면에서문제가 야기될 수 있고, 심지어 방류시 본 물질보다 높은 독성 물질이 배출되어 생태계뿐만 아니라 인간에도해로운 영향을 미칠 수 있다. 따라서 본 연구의 목적은 초기농도, UV 강도, pH, 그리고 질산염 (NO3-)이 비스페놀-A와 4-tert-옥틸페놀의 광분해의 속도에 미치는 영향과 분해부산물을 규명하는 것이다. 비스페놀-A의 초기농도가 2-40 mgL-1 그리고 4-tert-옥틸페놀의 초기농도가 0.5-5 mgL-1 로 증가함에 따라 비스페놀-A와 4-tert-옥틸페놀의 유사일차속도상수(k1)는각각8.5× 10-3 에서 3.7×10-3 min-1으로 그리고7.72× 10-2 에서 3.28× 10-2 min-1으로 감소하였다. UV 강도가3.65 × 10-5 에서 9.68 × 10-5 Einstein L-1 min-1 로 증가함에 따라더 많은 유기물이 π → π* 혹은 n → π* 상태가 되어비스페놀-A의 일차속도상수는 5.74×10-3 에서 14.50 × 10-3 min-1으로 그리고4-tert-옥틸페놀은 5.06 × 10-2 에서 12.07 × 10-2 min-1증가되었다. 두 물질은 비슷한 흡광도를 가졌지만비스페놀-A와 4-tert-옥틸페놀의 quantum yield는각각 0.035와 0.409 mol Einstein-1 이었다.비스페놀-A와 4-tert-옥틸페놀의 광분해는 용액의 pH를 유기오염물의 pKa (비스페놀-A(10.2) 4-tert-옥틸페놀(10.33))보다 높게 조절함에 따라상당히 상승하였다. 이는비결합 전자가 공명에 의해 π-system의 길이를 증가시킨 결과흡광도가증가된 결과이다.질산염은 빛과 반응하여 OH와 NO2라디칼을 발생시켜 유기오염물의 광분해를 빠르게 하였다. 하지만 일정량 이상이 첨가되면 일차속도상수는 오히려 점차적으로 감소하였다. LC/MS/MS를 이용한분해분산물 검출결과 질산염이 공존하는 광분해에서 비스페놀-A는 8개의 분해분산물이, 4-tert-옥틸페놀은 5 개의 분해부산물이 검출되었다. 질산염은 비스페놀-A의 광분해에서nitro-intermediate 발생을 유발하였다. 반면, 4-tert-옥틸페놀은의 광분해에서 질산염은 nitro-intermediate를 발생하지 않았다. 본 연구는 하∙폐수처리장과 질산염이 들어있는 자연수의 광분해에 의한 비스페놀-A와 4-tert-옥틸페놀의 광분해속도와 분해 메커니즘을 이해하는데 도움이 될 것이다.Bisphenol-A (BPA) and 4-tert-octylphnol (t-OP), known as endocrine disrupting compounds (EDCs), were hardly removed in conventional waste water treatment processes. Thepollutants should be removed from environment since they can cause adverse health effects such as breast cancer, hyperspadism,and testicular cancer. Photolysis can effectively remove organic compounds from water. However, if we apply photolysis as EDCs removal process at WWTPs without estimation of influencing factors and intermediates, it will cause energy, cost and by-product problems. In order to better understand and predict the behavior of BPA and t-OP photodegradation at aqueous, we investigated kinetics and degradation mechanism of photodegradation of BPA and t-OP using a photo-reactor system with UV.The objectives of this study are to examine the effects of initial concentrations, UV intensity, pH, and NO3- concentrations on the photodegradation of BPA and t-OP in aqueous and to identify intermediate products at photolysis of BPA and t-OP when NO3- is present. The pseudo-first-order rate constants (k1) of BPA and t-OP decreased from 8.5× 10-3to 3.7 × 10-3 min-1and from 7.72× 10-2 to 3.28× 10-2 min-1 with increasing initial concentration of BPA from 2 mg L-1 to 40 mg L-1 and t-OP from 0.5 mg L-1 to 5 mg L-1 because of complete absorption of the incident photon flux by higher initial concentration and the scattering effect. The pseudo-first-order rate constants of BPA and t-OP increased from 5.74× 10-3 to 14.50× 10-3 min-1 and from 5.06× 10-2 to 12.07 × 10-2 min-1, respectivelywhenUV intensity increased, whichcauses the more chemical to move π → π* or n → π*, from 3.65 × 10-5 to 9.68 × 10-5 Einstein L-1 min-1. The quantum yields of BPA and t-OP were found to be 0.0364 and 0.409 mol Einstein-1 in UV photolysis. The degradation efficiencies were significantly improved by increasing pH close to values which are 10.2 for BPA and 10.33 for t-OP. The degradation rate of BPA and t-OP enhanced with increasing nitrate concentration, up to 40 mg L-1 for BPA and 30 mg L-1for t-OP, and then decreased after this concentration. This result indicates that OH and NO2 radicals might play important rolesin photolysis of BPA, but at higher nitrate concentration, nitrate ion might act as a radical inhibitor.Intermediatesduring photolysis of BPA and t-OP were identified by usingLC/MS/MSin the presence of nitrate ion.Eight intermediates were identified from photolysis of BPA and five intermediates were identified from photolysis of t-OP in the presence with nitrate. The presence of nitrate induced the formation of nitro-intermediates in photodegradation of BPA. Also, the production and destruction of intermediates as well as degradation pathway were observed to examine the degradation behavior of BPA and t-OP. Our results can be helpful to understand the kinetics and removal mechanisms of BPA and t-OP by photolysis in the treatment process and in the natural water environment containing nitrate ions.Abstract i List of Figures vi List of Tables viii I. Introduction 1 1. Background 1 2. Information on the study compounds 3 3. Photolysis 8 4. Additives effects and degradation mechanism 12 5. Objectives 12 II. Materials and Methods 13 1.Chemicals 13 2.Intensity and quantum yield 13 3. Photoreactor 15 4. Analytical method 17 III. Results and Discussion 19 1. The initial concentration influence 19 2. UV intensity effects on direct photolysis 24 3. The effect of pH 31 4. The effect of NO3- 36 5. Intermediates 42 IV. Conclusions 52 References 54 국문초록 66 Appendix 69Maste