The concept of ‘self-assembly of organoclay nanotechnology’ is of significant importance for constructing hybrid nano-objects in equilibrium and non-equilibrium and the environment for practical applications, which have been extended to the nanotechnology due to the unique, remarkable physicochemical properties and multi-functions. The main objective of this research is to realize cationic organoclay nanotechnology by functionalized magnesium phyllosilicate (Mg clay) and its derivatives. We have developed organoclay nanotechnology based on positively charged organo-building blocks, i.e. self-assembly process to fabricate functional nanomaterials, to wrap anionic and heavy metal contaminants, and to selectively interact with microalgae e.g. red tid as an algicidal agent. In detail, high-density amine groups of Mg clay functioned as template sheathed materials of J-aggregate rod structure by self-assembly of TPPS (porphyrin monomers). Furthermore, the gallery of nanomaterials composed of organoclay and anionic contaminants was reassembled for water treatment. This novel application of cationic organoclay into environmental area opens a new window to treat for a variety of negatively charged toxic chemical from water. Furthermore, binding affinity of protonated exfoliated dispersion of Mg clay with cadmium and lead was applied with an inexpensive and environmental friendly soil flushing agent. In respect to microoalgae with this organoclay, ammonium property of cationic organoclay showed selectively algicidal activity, resulting in inhibition of algal bloom while little affecting other living microorganisms in sea water, which experiments were conducted batch, microcosm, and mesocosm.
As synthesis of organoclay described herein was simple technology to prepare diverse functionalized side chains and various backbone metal ions such as $Mg^{2+}$, $Al^{3+}$, $Fe^{3+}$, $Cu^{2+}$ etc. in ambient condition via sol-gel reaction: hydrolysis and condensation. In particular, using 3-aminopropyl triethoxysilane (APTES) precursor as functional group, which induced sol-gel reaction autocatalytically and formed with high-density amines by one-pot method, has advantages over conventional solution syntheses in terms of eliminating the complications asso-ciated with more two steps and avoiding the post-addition of base (NaOH). Except for magnesium backboned organoclay, we have tried its derivatives by different combination of metal ions and organo-functionalities. As a result, we have established the organoclay library. The different metal ions affected in organoclay particle size, provided that organo functionality is used APTES.
Based on unique property of prepared organoclay, focusing on Mg clay, we have constructed organoclay sheathed J-aggregate tapes by wrapping organoclay building-blokcs highly exfoliated, closely to water-dissolved in water media. Because J-aggregate formed by acid treatment of TPPS (porphyin monomers) is self-assembled rod structure, J-aggregate is retained in limited in acidic condition by secondary interaction of driving force. J-aggregate is well-known to photosynthetic system to increase light harvest and collection substrate. In order to utilize J-aggregate structure in neutral media, we have focused on stabilization of J-aggregate with cationic orga-noclay when considering negatively charged (sulfonate side functional groups) outer surface of J-aggregate. However, organoclay stabilized J-aggregate still disaseembled ca. pH 5.0, this result is due to protonation of amine group of organoclay is affected competition of $H^+$ and decrease in zeta potential, even though positively charge surface of organoclay still maintained. Therefore, we can consider another approach to use titanium precursor to stabilize J-aggregate by transformation of amorphous titanium to crystalline structure (anatase) by hydrothermal treatment with retention of chromophores of J-aggregate arrangement. Successfully we developed nice J-aggregate nanofilament using titanium template to apply as a photocatalyst, resulting in increase in rate constant of phenol degradation from water. From this result, future research can be expanded to use J-aggregate nanofilment to decorate metal nanoparticles for proper usages, or to develop photocatalytic reactor to use sun-light.
In environmental water treatment, cationic organoclay will be applied into negatively charged anionic contami-nants as a novel adsorbent. Oppositely conventional organoclay, which is catnionic surfact modified with clay to present cationic property and hydrophobicity to adsorb hydrophobic toxic contaminants and oxyanions, because of no naturally occurring clay with positive charge. Arsenate and chromate among toxic oxyanions, and cyan source of unstable form of ferricyanide, were simply treated by reassembly process between organoclay and anionic contaminants. All anionic contaminants were precipitated with fast reaction time effi-ciently. The final product of precipitate is characterized to layer restacked structure. The applications of cationic organoclay for water treatment can be further applied to negatively charged materials ($F^-$, $NO_3^-$, $PO_4^{3-}$) and to treat for heavy metal pollutants contaminated soils via combination of other technologies.
In viewpoint of ammonium property of this, we have an idea to apply to kill harmful algae, or red tide selective-ly. In Korea, Red tide has damaged to aquacultures in Korea economically for past decades. To overcome this problem, yellow loess had been spreaded in tonnage. However, this clay was significantly damaged benthic eco-system with less efficient death of harmful algae. Nowdays, one of reduction method of clay dosage, cationic surfactant modified clay has been developed efficiently to treat harmful algae. But this method still is limited in application because of sedimentation of clay into bottom in sea water. As another method to treat harmful algae, spreading of ammonia killed harmful algae selectively by lysis cell membrane. The demerit of this tech-nology is toxicity of ammonia to spread into ecosystem into marine environment. As a result, ammonia mixed with clay to reduce the toxicity has been reported with good result. Therefor, history of harmful algae treatment leads to desire of ammonium organoclay to apply into red tide. Desipite the unclear mechanism of algicidal ac-tivity of cationic organoclay selectively, we had superior results along with microcosm. And mesocosm. In addi-tion, we are planning ecotoxicological effect and life-time in environmental long-exposure of organclay.
In conclusion, novel cationic organoclay serves as the multifunctional material in terms of acting as covalent bonding for fluoresce dyes with high-density amine functional groups or template to reaction with parent rod-shaped porphyrin nanostructure in the design and fabrication of nanomaterials, assembling, and precipitating with target anionic contaminants and heavy metals, and finally interacting with microorganisms in the process of algicidal activity by lysis of membrance of microalgae.
일반적으로 유기점토라고 하면 천연 음이온성 점토에 양이온성 계면활성제를 이온 치환을 하여 친유성과 양이온성 성격을 부여한 것을 칭한다. 이는 무기물로 이루어진 점토를 물리적으로 개질할 수 밖에 없는 한계성 때문이었다. 하지만 전구체가 유기체와 무기물로 동시에 이루어진 물질로 유기점토를 손쉽게 합성할 수 있다면 그 응용 분야는 다양해질 수 있다. 이에 본 연구에서는 가 양이온인 마그네슘 이온, 구리 이온 그리고 가 양이온인알루미늄 이온, 철 이온을 중심으로aminopropyl chain이 샌드위치 형태로 된 phyllosilicate 계열을 합성하였다. 이는 amine grou이 수용액에서 protonation이 되어서 암모니아 성향을 띠게 되고, 양이온으로 서로 반발력이 생기게 되어서 물에 분산성이 좋은 sheet 형태로 존재하게 된다. 하지만 sheet의 크기 분포는 마그네슘으로 만든 phyllosilicate (유기점토)가 제일 작으며, 용해도가 제일 뛰어났다. 물론 다른 3가지 종류의 유기점토도 물에 대한 분산성은 좋으나 sheet의 크기가 상대적으로 크고 이에 따른 물에 대한 용해도가 떨어졌다. 특히나 amine 밀도가 굉장히 높기 때문에 이의 응용처가 많을 것으로 쉽게 짐작이 된다. 현재까지는 Bristol 대학의 Stephen Mann 그룹에서 lipid, DNA, enzyme, peptide의 bimolecule과의 bio-nanocomposite 연구에 국한되어 왔고, 환경분야에로의 응용은 전무후무하다.
먼저, 물에 대한 용해도가 좋고 양이온 성향을 보이는 성질을 이용하여, 음이온성 오염물질인 oxyanion 계열인 arsenic, chromate 및 ferricyanide를 self-assembly 공정을 통한 침전으로 제거하는 실험을 하였다. 수분 내에 높은 제거 효율을 보였으며, 유기물질이 있는 상황에서는 유기물질도 함께 제거되는 결과를 얻었다. 하지만 유기물질의 경우, 분자량이 bulk하기 때문에 다른 oxyanion 물질 제거에 저해 작용을 하였다. 이와 더불어 전자 폐수의 주요 성상인 fluoride, nitrate, phosphate의 제거도 동시에 실험하였다. 물에 대한 용해도가 좋기 때문에 침전에 의한 제거가 불가능하여, filtration 방법을 사용하였다. Phosphate의 제거 효율이 높게 나왔으며, 추후에 유기점토에 잔류하는 chloride 이온의 양을 줄이는 방안에 대한 연구가 필요할 것으로 보인다. Chloride 이온이 다른 ion 물질들과의 결합을 방해하기 때문이다.
나아가 양이온성 유기점토의 수처리에 대한 응용 뿐만 아니라, 토양의 복원에도 이용할 수 있는 가능성을 제시하였다. 중금속으로 오염된 토양의 경우, 기존의 산이나 EDTA와 같은 chelan는 사용후 처리와 토양의 생태계를 파괴하는 문제점이 있었다. 이에 비교적 값이 저렴한 유기점토를 이용하여 중금속으로 오염된 토양 복원의 flushing제로써의 사용이 적합함을 알 수 있었다. 디젤로 오염된 토양의 경우에는 양이온성 유기점토를 사용할 수가 없었다. 인공적으로 합성한 신물질이기 때문에 독성 등 환경에 대한 평가가 선행되어야 하기 때문이다. 따라서 유류분해 미생물을 고정화하기 위해서 일반 점토인 bentonite를 사용하여 현장실증에 사용하였다.
마지막으로 유기점토의 암모니아성 성질을 이용하여 적조를 선택적으로 죽이는 실험을 수행하였다. 아직 암모니아성 물질이 선택적으로 적조를 죽이는 mechanism은 명확하지 않으나, 암모니아가 가지는 독성을 clay 형태로 인한 독성 저해 효과를 가져올 수 있으며, 물에 대한 분산성이 좋기 때문에, 기존의 황토가 가진 문제점을 해결할 수 있을 것으로 보인다.
본 연구에서는 양이온성 유기점토의 환경분야에로의 다양한 사용가능성을 제시해주며, 향후 유기점토의 환경독성평가 및 수명에 대한 연구가 추가적으로 더욱 필요하다.
