Setup for preparation of silver chloride film. Figure 2. Experimental setup for photocatalytic degradation. 

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Context 1

... were fabricated through precipitation reac- tion between sodium chloride solution and silver nitrate solution which was first frozen using liquid nitrogen. The detail procedures are as follows: A PVC tube (with I.D. of 1.8 cm and length of 3 cm) was sealed with Teflon film on one end (see Figure 1). A 0.2-mL of known con- centration of AgNO 3 solution (8.3 M, 6.3 M, 4.2 M, or 2.1 M) was added into the tube. A 6061 aluminum plate was first immersed in liquid nitrogen, and brought con- tact to the closed end of the PVC tube to freeze AgNO 3 solution into solid state. Then, a 3-mL of NaCl solution (5.4 M) was added into the PVC tube. The contact of NaCl solution melts solid state of AgNO 3(aq) to liquid state initiating precipitation reaction to form AgCl. Af- ter pre-determined reaction time (10 min, 12 hrs, and 24 hrs), residual NaCl solution on the top of SCTF was dis- carded, and the film was rinsed with DI water for 5 times. After the Teflon film on the bottom of the PVC tube was removed to drain the un-reacted AgNO 3 solution, the bot- tom of SCTF was rinsed with DI water for 5 times. The film was dried in oven at 100 °C for 8 hours. The finished products have apparent area of 2.54 cm 2 and weight of about 0.036 g. Because the band gap of AgCl is within 3.1 ev~3.3 ev corresponding to light wavelength of 375 nm~400 nm, the whole preparation process was done un- der yellow light to prevent photolysis ...

Context 2

... 3 (T1) shows the top surface of SCTF formed at reaction time of 10 min, indicating that newly formed silver chloride grains are small and the film has many small holes. As solution of sodium chloride contacting the melting solution of silver nitrate, AgCl is rapidly pre- cipitated and grains of silver chloride are relatively large due to very high concentration of both solutions [16]. At this moment, they are quickly piled into continuous thin films. Many small holes are formed due to different ori- entation of AgCl grains stacked together. Figure 3 (B1) shows the microstructure of bottom surface of SCTF which has the similar small grains as those on the top surface. In addition, some rod-like struc- ture formed by piling up of many tiny particles can also be found on the bottom surface. After the continuous thin film is formed, it will be a layer of obstruction for colli- sions between chloride ions and silver ions. At the bottom surface of SCTF, chloride ions can only diffuse through the tiny gaps/holes of films (such as grain boundary), and then it causes the decrease of ion concentration. At the same time, solid silver nitrate solution slowly melts into liquid. Coupled with the super-cooling effect and low aqueous solubility of silver nitrate solution under extre- mely low temperature, relatively small grains of silver chloride are generated, and are incubated on the bottom surface of thin film as seeds. At this time, small particles of AgCl are precipitated continuously, and piled into rod structure at the bottom surface by priority directions. With the reaction time of 12 hours (Figure 3 (T2)), the most of the small holes on the top surface are disap- peared and the grains have become larger and denser, in- dicating the small holes were filled by grain growth. In addition, the surface has many irregular stripes which are the contraction trace left by diffusion during grain growth process. The bottom surface of the film is shown in Fig- ure 3 (B2). Apparently, more rod structure could be found, and the size of grains has become larger. As shown in Figure 3 (C2), the film growths thicker at around 100 mm, and the holes have been filled gradually became smaller and fewer. In addition, the bottom surface with rod structure can be ...

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... SEM images of the top surface under various AgNO 3 concentrations are shown in Figure 4 (T1~T4). Compared with the top surface of SCTF made by AgNO 3 of 8.4 M (Figure 4 (T1)), the morphology of films made at lower AgNO 3 concentration of 6.3 M (Figure 4 (T2)) shows a very different crystal structure. The tiny rod structure is composed of small grains, and boundary be- tween crystals is not obvious. When the concentration of silver nitrate solution is lowered to 4.2 M (see Figure 4 (T3)), the rod structure is less obvious. With 2.1 M of silver nitrate solution, the rod structure (Figure 4 (T4)) appears again, and more apparent than those in the con- dition of 6.3 M. Some of grains proliferated with each other resulting in that the links between grains are much denser, and the grain boundaries become blurs. When the concentration of silver nitrate solution is lowered to 2.1 M, the rod struc- ture disappears and is replaced with many tiny grains piled on the surface (as shown in Figure 4 (B4)). Com- parison of the size of grains under 2.1 M with those made under 6.3 M and 4.3 M, the grain size is relatively lar- ger and less denser. Clearly, no crystal precipitated on the bottom surface, and those grains attached to the bot- tom surface are formed through heterogeneous nuclea- tion. From the cross section view shown in Figure 4 (C1)~ (C4), thickness of the films are not much ...