Coordination Compounds For The Treatment Of Dye Wastewater: Preparation And Application

In recent years,the removal of organic pollutants from wastewater has received more and more attention.Considering that organic pollutants are generally stable to light,heat and oxidizing agents,they might exert high potential risk to the environment and living things.Numerous materials have been used to treat contaminated water before drainage,such as nano-adsorbent,TiO₂ photocatalyst and so on.Although these materials have a good effect on the treatment of the waste water,it is not benefit to study the structure-function relationship between materrials and pollutants.So,it is essential to explore newly environmental remediation materials to solve the water pollution problem.Coordination compounds are emerging class inorganic-organic hybrid materials,which are constructed by metal ions and organic ligands.Because of their diverse compositions,easily tailored structures,tunable surfaces and active sites,coordination compounds have been widely applied in the field of adsorption,fluorescence,catalysis,chemical sensors,and so on.For the environmental remediation,coordination compounds have been utilized as an efficient adsorbent for the organic pollutants removal in wastewater,or as heterogeneous photocatalysts to conduct organic pollutants degradation,CO₂ reduction and Cr（VI）reduction under UV/visible/UV-visible light irradiation.In this work,based on the crystal engineering principle,several coordination compounds of different structure and adsorption /photocatalytic properties have been synthesised.And the related reaction mechanisms have been explored.The experimental results are briefly described as following:1.The silver-based coordination polymer [Ag₄（dpe）₄]·（butca）·13H₂O（CP 1）（dpe = 1,2-di（4-pyridyl）ethylene and H₄ butca = 1,2,3,4-butanetetracarboxylic）,as an efficient adsorbent,had been synthesized in aqueous alcohol/ammonia by slow evaporation at room temperature and used to conduct adsorptive uptake of four typical organic dyes including anionic methyl orange（MO）and anionic congo red（CR）,cationic methylene blue（MB）and cationic rhodamine B（Rh B）.The results demonstrated that CP 1 could remove anionic dyes from the aqueous solution more efficiently than cationic dyes,in which the maximum adsorption capacity of CP 1 towards MO and CR was 779 mg/g and 739 mg/g.The adsorption process of MO by CP 1 fitted well with the pseudo-first-order.Moreover,Langmuir and Freundlich isotherm models fitted better to the obtained experimental data.The adsorption reaction of MO was endothermic,spontaneous processes,and tended to be disordered,which could be affirmed by thermodynamic functions such as（35）G⁰,ΔH⁰ and ΔS⁰.CP 1,as a stable adsorbent,could efficiently separate MO and MB from their mixture solution,which was further confirmed by self-made SPE column.Additionally,its antibacterial property can prevent the membrane being impacted by bio-colonization.2.[Ag₄（dpe）₄]·（btec）（CP 2）and [Ag₄（bpy）₄]·（btec）·12H₂O（CP 3）（dpe = 1,2-di（4-pyridyl）ethylene,bpy = 4,4′-bipyridine,and H₄ btec = 1,2,4,5-benzenetetracarboxylic acid）had been synthesized by novel organic ligands,and characterized by single crystal X-ray diffraction（SCXRD）,Fourier transform infrared spectroscopy（FTIR）,CNH elemental analysis（EA）,UV-Visible diffuse reflectance spectra（UV-Vis DRS）and luminescence spectroscopy（PL）.Both coordination compounds 2 and 3 are composed of 1D infinite cationic [Ag/dpe（bpy）]n n+ chains and discrete btec4-anions.The three dimensional supramolecular structure of CP 2 and CP 3 were built up of cationic sheets formed from [Ag/dpe（bpy）]n n+ via weak Ag…Ag and Ag…N interactions,and anionic btec4-sheets by electrostatic interactions,π-π interactions and hydrogen-bonding interactions（except for CP 2）.Compounds 2 and 3 exhibited good luminescence and photocatalytic performance to decompose methyl orange（MO）under UV light irradiation.3.Three novel coordination compounds based on transition metals like Co（II）,Cu（II）and Mn（II）,namely [Co2（bpy）₂（nbda）₂（H₂O）₂]·2H₂O（denoted as CP 4）,[Cu2（bpy）₂（nbda）₂（H₂O）₂]·2H₂O（CP 5）,[Mn2（bpy）₂（nbda）₂（H₂O）₂]·2H₂O（CP 6）,（where bpy = 4,4′-bipyridine,H₂ nbda = 2,3-norbornanedicarboxylic acid）,were synthesized under hydrothermal conditions,and characterized by single crystal X-ray diffraction（SCXRD）,CNH elemental analyses（EA）and Fourier Transform infrared spectroscopy（FTIR）.CP 4-6 were isostructural and crystallized in the monoclinic space group C2/c.The metal atoms of CP 4-6 were linked by typical bidentate bpy ligands into two adjacent 1D [M1（bpy）]n²ⁿ⁺ and [M2（bpy）]n²ⁿ⁺（M = Co（II）,Cu（II）,Mn（II））,which were further joined by completely deprotonated nbda2-ligands into 2D [M2（bpy）₂（nbda）₂]n sheets.Finally,three-dimensional supramolecular frameworks were constructed with the aid of the hydrogen bonding interactions.CP 4-6 exhibited different photocatalytic degradation ability to decompose methylene blue（MB）and methyl orange（MO）under UV light irradiation.Additionally,a possible photocatalytic mechanism HOMO-LUMO was proposed and discussed,which was further confirmed by radicals trapping experiments using isopropanol as radical scavenger.