Controllable Synthesis Of Silver Bromide Via A B-Z Reaction

Nonlinear chemistry is the study of various temporally and spatially ordered structures formed when a chemical system is far from the thermodynamic equilibrium state or the research on the nonlinear dynamic behaviors.Among them,the Belousov-Zhabotinsky(B-Z)reaction is the most studied chemical system,the concentration of each component in B-Z reaction(such as Br~-)can spontaneously and periodically change versus time or space,which offers an ideal model reaction for the controllable synthesis of silver bromide(AgBr)via kinetic manipulation.However,due to current controlled synthesis of AgBr is limited to the low-indexed morphologies favored by thermodynamics such as cubes,octahedrons.To solve this problem,it is necessary to fundamentally break through the thermodynamic difficulties in generating high-indexed crystal planes,because the high-indexed crystal planes will be energetically unfavored.Therefore,this study focuses on the synthesis of silver bromide crystals coupled with the B-Z reaction,utilizing nonlinear dynamics of B-Z reaction to pull the reaction away from the thermodynamic equilibrium state,so that the growth environment of AgBr is in a high-energy thermodynamically unstable state.Two types of concave AgBr crystallites were successfully synthesized with different shapes:star shape and concave cube(both possess an average size of 1?m).Studies have shown that when high-indexed crystal faces of AgBr are formed in a thermodynamically unstable state,the system does not require additional stabilizers to maintain the high-energy crystal facets.The intermediate product of the B-Z chemical reaction,benzoquinone and its derivatives,can effectively stabilize high-index faceted AgBr crystals.The specific research results are as follows:1.Controllable synthesis of AgBr concave cubes:The controllable synthesis of 1?m cubic concave AgBr can be achieved by manipulating the reaction kinetics of a zero-dimensional homogeneous chemical oscillation system.It was found that the optimal synthesis conditions for cubic concave AgBr with high-indexed crystal facets must be located in the chemical oscillation regime.This is because the oscillation zone is at a high-energy thermodynamically unstable state,which is conducive to the growth of high-index faceted crystals.This work also explored the influence of acetonitrile concentration on the oscillatory behaviors,suggesting that the increase of acetonitrile concentration can cause a sharp decrease of oscillatory period,changing from 43.29 s without acetonitrile to 9.99 s with 20 m L acetonitrile.Furthermore,the induction period and the oscillation life is also shortened.This is probably due to the molecular mobility of acetonitrile is much faster than that of water.In addition,the influence of the oscillation system on the morphology of silver bromide was studied,and it was found that in the presence of high concentration of acetonitrile(20 m L),the synthesis of cubic concave silver bromide crystalline was relatively more uniform.2.Controllable synthesis of star-shaped AgBr:The controllable synthesis of star-shaped high-index faceted AgBr was carried out in a 1,4-cyclohexanedione-sulfuric acid-sodium bromate reaction-based two-dimensional pattern formation system.Star-shaped AgBr crystals were successfully synthesized under the control of pattern dynamics caused by Turing bifurcation.Through the study of in-situ spatio-temperal pattern dynamics,it was found that when the spacing of pattern waves induced by the B-Z reaction is very small,the residence time at high-energy unsteady state is very short,forming a conventional(100)crystal faceted AgBr with a size of about 100 nm.When the dynamic parameters of the pattern are adjusted to a wider spacing,more and more obvious dynamic behaviors of the pattern.When the pattern confronts an unstable state,which is at a high-energy state,the non-steady state residence time will be greatly enlarged,so as to ensure that the high-index faceted AgBr has sufficient time to nucleate and grow,and finally form 1?m silver bromide.Through the investigation of the relationship between different AgBr morphologies and pattern kinetics,it was found that sulfuric acid concentration is the most sensitive pattern dynamics parameter:when the sulfuric acid concentration is 0.5 mol/L,the dynamic behavior of the pattern results in a 1?m star-shaped AgBr;While the sulfuric acid concentration is as high as 4.0 mol/L where the pattern does not appear,the as-synthesized silver bromide is a conventional nanocube sized around 100nm,which is favored by thermodynamic regulation.Finally,through in-situ pattern dynamics studies and ex-situ characterization of intermediate products,it was confirmed that the controllable synthesis of star-shaped high-index faceted AgBr crystalline depends on the pattern kinetics and the pattern wave spacing.