| The species structure of aluminum salt hydrolysates is not only the key to reveal the flocculation interaction mechanism between Al-series flocculants and colloidal particles for objectively screening high-efficiency flocculants in water pollution control chemistry,but also the key to understand the transformation and transport law of aluminum for effectively preventing aluminum pollution in environmental chemistry.It is also the key to understand the biological metabolism of aluminum for effectively preventing aluminum poisoning in biochemistry.And it is still the key to explore the genesis and dissolution mechanism of aluminum-containing mineral for guiding prospecting,scientifically managing the mining operation,and controlling the transformation and transport of aluminum from the source in geochemistry.There is no a common consensus about how an aluminum monomer is evolved into aluminum hydroxide in aqueous solution,due to the limited number of known aluminum species structures.The reason is that various aluminum species coexist and their distributions dynamically change with temperature and solution composition in a hydrolyzed solution.So it is difficult to isolate pure polyaluminium compounds from it and is harder to obtain a large enough single-crystal for structure solving.The researches and practices of our group for 20 years have proved that,"phase diagram controlling?pure compound isolating?single-crystal culturing?structure solving?mechanism speculating?structure-activity correlating" is an effective technical route for synthesizing more polyaluminum compounds,obtaining more aluminum species structures,and then speculating their evolution mechanisms.In this paper,the first five new polyaluminum compounds were synthesized by respectively adding H2(1,5-NDS)(NDS represents naphthalene disulfonate anion),Na2(2,6-NDS),Na2(2,7-NDS)and Na(PTS)(PTS represents p-toluenesulfonate anion)into the AlCl3-Al(OH)3-H2O ternary systems formed by spontaneously hydrolyzing the AlCl3 solution to different degrees(medium basification degree B=[OH]/[Al]=0.6?1.4)with Al powder at 50??80?.To capture the polyaluminum species in these solutions,the composition of the solutions was controlled according to the mind of tetrahedral phase diagram by regarding each capturing reagent mentioned above as the fourth component.After slowly evaporated and crystallized for 7?90 days at room temperature or 0?,respectively,their single-crystals were obtained.The single-crystal of the sixth polyaluminum compound was obtained by hydrothermal aging ethanol and ethylene glycol solution of P-Al13 chloride([Al13(OH)24(H2O)24]Cl15·13H2O)at 125? for 20 hours.The final two new polyaluminum compounds were synthesized by respectively adding Na2(2,7-NDS)and Na2(2,6-NDS)solutions into the AlC13-CsCl-Al(OH)3-H2O quaternary systems formed by forcedly hydrolyzing the AlCl3 solution to B=2.4 with CsOH solution at 80? for 24h and then hydrothermal aging at 125? for 16h,after slowly evaporated and crystallized at room temperature for 3 months their single-crystals were obtained.X-ray structural analysis results show that their structural formulas are:[Al2(OH)2(H2O)8](1,5-NDS)2-4H2O,[Al8(OH)14(H2O)18](2,6-NDS)4Cl2·18H2O,[Al8(OH)14(H2O)18](2,7-NDS)4Cl2·27H2O,[Al13(OH)24(H2O)24](PTS)13Cl2·28H2O,[Al30.5O8(OH)61.5(H2O)23](2,6-NDS)4C16-47.5H20,[AlO4Al12(OH)12(OC2H4OH)12]Cl7·H2O,[(2,7-NDS)2Cs(H2O)7AlO4Al12(OH)24(H2O)12](2,7-NDS)2·11H2O and[Al26O8(OH)50(H2O)20](2,6-NDS)6·57H2O.The structure of Al2([Al2(OH)2(H2O)8]4+)in[Al2(OH)2(H2O)8](1,5-NDS)2-4H2O(internal basification degree Bi=1.00)is that two A106 octahedra are linked together by edge-sharing,it was captured from the polyaluminum chloride solution of B=0.6,indicating that Al2 species exist in the solution of a low medium basification degree.The structure of Al8([Al8(OH)14(H2O)18]10+,Bi=1.75)in[A18(OH)14(H2O)18](2,6-NDS)4Cl2·18H2O and[Al8(OH)14(H2O)18](2,7-NDS)4Cl2·27H2O can be regarded as that four A106 octahedra are linked together by edge-sharing forming a "plank",and then additional four AlO6 octahedra suspend onto the perihery of the "plank".They are the first three examples in which the polyaluminum species belonging to "Plank-suspengding" structures composed of A106 octahedra only without any A104 tetrahedra were captured by NDS2-anions from spontaneously hydrolyzed AlC13 solutions,indicating that more little-known new polyaluminum species in spontaneously hydrolyzed unsaturated solutions rich in polyaluminum species can be captured by NDS2-,that is,a new pathway of enriching the varieties of polyaluminum compounds and the structural types of aluminum species was found.The structure of P-Al13([Al13(OH)24(H2O)24]15+,Bi=1.85)in[Al13(OH)24(H2O)24](PTS)13Cl2·28H2O is that seven A106 octahedra are linked together by edge-sharing forming a seven-Al "plank",and then additional six A106 octahedra suspend onto the perihery of the "plank" upper and lower alternately with an average inward turn angle of 25.5°.This "Plank-suspending" structure is similar to that of those polycations in chloride,bromide,iodides,and nitrates of P-Al13 previously synthesized by our group,in which the average inward turn angles of the six external A106 octahedra are ranging from 21.1° to 26.2°.It indicates that the spatial orientation of the external AlO6 octahedra in P-Al13 can be "freely" adjusted according to the size and shape of the counteranions,and the A106 octahedra suspended onto the "plank" only by using two vertexes have greater swinging abilities.It provides new evidence for improving the SSSS(Splicing,Suspending,Swinging and Slipping)model and theory of polyaluminum species proposed by our group.In addition,When NDS2-anions were added to a polyaluminum chloride solution of B=1.0,the precipitated product is naphthalene disulfate chloride of Al8,however,when twice of the PTS anions were added to the same solution,the precipitated product is p-toluenesulfonate chloride of P-Al13.It shows that the two polyaluminum species having the same "Plank-suspending" structure(the difference of their Bi values is only 0.1)coexist in the polyaluminum chloride solution,and the single-phase crystalline regions of their compounds in the tetrahedral phase diagram should be adjacent to each other.These results provided direct evidences for drawing the evolution mechanism that A1 monomer([Al(H2O)6]3+)gradually evolves into P-Al13 through Al2,Al4,and Al8.The structure of gly-?-K—Al13 in[AlO4Al12(OH)12(OC2H4OH)12]Cl7·H2O is the result that twelve OH and twelve H20 of ?-K-Al13 were replaced by twelve OC2H4OH-.It's worth noticing that there are not Al(OH)4 ions in the raw materials(chloride of P-Al13,ethanol and ethylene glycol)for synthesizing the chloride of gly-?-K-Al13 obviously,however,gly—?-K-Al13 had an A104 core can be formed by aging the P-Al13 under the hydrothermal condition in such a weak alkaline environment of spontaneous hydrolysis.That is,a direct evidence supporting the judgment that the P-Al13 of "Plank-suspending" structure can be converted into the?-K—Al13 of“core-shell”structure by self-assembly,which was previously drawn based from the changes of 27Al NMR information when chloried of P-Al13 were re-dissolved in water,was found.Therefore,it is unnecessary to create a micro-environment for forming the A104 tetrahedral core in advance with a strong alkali such as NaOH etc,an A104 tetrahedron can be transformed from an A106 octahedron by self-assembly when a "core-shell" structure is needed to build.In other words,Forced hydrolysis is not the only way to form a "core-shell" structure.The structure of 2,7-NDS-Cs-??K-Al13([(2,7-NDS)2Cs(H2O)7A104A112(OH)24(H2O)12]4+)in[(2,7-NDS)2Cs(H2O)7A104A112(OH)24(H2O)12](2,7-NDS)2·11H2O is equivalent to that two different CsO8 caps in which two sites were statistically occupied by one Cs+ion are capped on one ?-K-Al13,however,the positions where the caps are capped on are not only different from that in Na-?-K—Al13 in which the Na06 cap is capped on the outside of the triangular pit of the A13 unit that was rotated 60°,but also different from that in 2,7-NDS-Na2—?-K—Al13 in which one NaO6 cap is capped on an A106 octahedron located on the outside of the Al3 unit(rotated 60°)by face-sharing,the other NaO6 cap is put on another unrotaed Al3 unit by edge-sharing.Here,one CsO8 cap with a 2,7-NDS ligand is capped on an A106 octahedron located on the outside of an unrotated Al3 unit by face-sharing,the other CsO8 cap is connected at a corner of the triangular pit on the same unit by vertex-sharing,and there is not any coordination polyhedron connected on the Al3 unit which was rotated 60°.The ?-K—Al13 with two Cs caps are connected by two ?3-2,7-NDS forming the basic repeating unit that forms a continuous 2,7-NDS-Cs—?-K—Al13 infinite chain by sharing the coordination water molecules(in which two sites are statistically occupied by one O atom)on its both sides(See Figure 4.9 in main text).The discovery of this novel and unique structural manner means that the conversion from?-K-Al13 to ?-K—Al13 does not require the help of a NaO6 cap(many provious literatures believed that the rotation of the Al3 unit needed the help of a NaO6 cap),the temperature of hydrothermal treatment is the driving force that causes the Al3 unit to rotate.The structure of Al26 in[Al26O8(OH)50(H2O)20](2,6-NDS)6·57H2O is that two?-K—Al13 connected to each other by sharing two vertexes,that is,a vertex on an unrotated Al3 unit of one ?-K—Al13 is sharing with the rotated Al3 unit of another?-K—Al13 and vice versa(See Figure 4.15 in main text).It is similar to that reported in[Al26O8(OH)50(H2O)20](2,6-NDS)6·12.4H2O,but the number of interstitial water in the compound is quite different,so it is a new polyaluminum compound.The appearance of Al26 species provides direct evidence for the "K—Al13 aggregation"model.The structure of Al30.5([Al30.5O8(OH)61.5(H2O)23]14+)in[Al30.5O8(OH)61.5(H2O)23](2,6-NDS)4Cl6·47.5H2O is equivalent to the result that firstly two pairs of H2O molecules in the first-class active area and one H2O molecule in the second-class active area were hydrolyzed and totally five protons(four in the first-class active area and one in the second-class active area)were removed in the waist of "Al30"([A130O8(OH)56(H2O)26]18+reported in literatures,whose structure was that two Al-?-K-Al13 were connected together by two A106 octahedral monomers by sharing respective four vertexes,and the Al-?-K-Al13 is the result that the NaO6 octahedron in Na-?-K—Al13 was replaced by an A106 octahedron),then a five-coordinated Al nucleus with a site occupancy of 1/4([Al1/4(OH)2[(OH)1/4]2(H2O)])was combined between each pair of OH-groups formed by deprotonation on the both sides of the first-class active area,finally they were connected with each other by edge-sharing forming an infinite long chain with[Al30.5O8(OH)61.5(H2O)23]14+as the basic repeating unit(See Figure 4.20 in main text).It shows that a long chain with "core-shell"structure can also be captured from a spontaneously hydrolyzed aluminum solution,and this novel structural manner has never been reported.However,this does not mean that the A104 tetrahedra would definitely be induced out by adding sodium naphthalene disulfonate to a spontaneously hydrolyzed aluminum solution,because the Al2 and Al8 naphthalene disulfonates precipitated from the spontaneously hydrolyzed aluminum solutions do not have A104 tetrahedron.Therefore,which kinds of hydrolysates will be precipitated from a hydrolyzed aluminum salt solution at a certain temperature is determined by the positions where the chemical compositions of the solution of the system locate on in the phase diagram.The discovery of the Al30.5 infinite chain not only directly verified the scientificity of the local basification degree symmetrical equalization(LEDSE)principle proposed by the our group,which predicts that there are two classes of hydrolytic active areas at the waist of "Al30",but also it becomes the polyaluminum species whose hydrolyzation degree(Bi=2.541)is higher and more close to Al(OH)3 than S-A132(Bi=2.375,reported by our group)in the "core-shell" structures found so far.It also provides important clues for explaining the interaction mechanism between Al-series flocculants and colloidal particles and obtaining a more accurate coagulation mechanism.The discovery is of great significance for a deep understanding of the formation and transformation laws of polyaluminum species in hydrolyzed aluminum salt solutions,and communicating the relationship between spontaneous and forced hydrolysis.In this paper,most crystalline regions of the solid-liquid equilibrium isothermal phase diagram of AlCl3-Al2O3-H2O system at 125? under hydrothermal conditions were successfully measured by combining the wet slag method and the synthesis system method,using the special functions of the preparative high-pressure reactor system designed by the our group and manufactured by a company,that has online filtering and sampling,online distillating and concentratiing,and online feeding in the process etc.functions,using efficient and accurate solution's X-ray fluorescence analysis method replaced the traditional manual volumetric and gravimetric analysis method.It provides a control basis for isolating pure polyaluminum compounds from complex polyaluminum chloride solutions under hydrothermal conditions,it also build a foundation for further stadying on the tetrahedral phase diagram of the quaternary system such as AlCl3-Al2(SO4)3-Al2O3-H2O system under hydrothermal conditions. |
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