User:Andchemist/sandbox

1. Links: This tentative wiki site captures a good view on SECM which is a surface/interface characterization technique on the basis of electrochemistry. In this context there might be few other popular techniques which could be mentioned like X-ray photoelectron spectroscopy (XPS), Electrochemical Impedance Spectroscopy (EIS) and Potentiodynamic Polarization. Probable Wiki links author could attach here: X-ray photoelectron spectroscopy, Electrochemical Impedance Spectroscopy (EIS)

2. The page is well-written and well-understood except few following points:

a)" Simultaneous experiments by Allen J. Bard using an Electrochemical Scanning Tunneling Microscope (ESTM) demonstrated current at large tip-to-sample distances that was inconsistent with electron tunneling." It is not well understood how electron tunneling and faradic current are correlated.

b) Diffusion-limited current and steady state current - are they same? If yes, this should be explicit for general readers.

c) The equation for steady state current doesn't have any term which implicitly/explicitly contains distance between the tip and substrate. Thus public might the curious about the fact how "the tip is moved closer to the surface and changes in current are measured." Also in this equation D is the diffusion coefficient of species O, "species O" should be mentioned.

d) electrode sheath diameter, rg should be well-explained.

e) positive and negative feedback loop should be explained more clearly like: With UME far from the substrate diffusion of O gives rise to steady state current iT, ∞, with the UME placed near an insulating substrate iT, ∞ < iT, with the UME placed near conductive substrate positive feedback leads to iT, ∞ > iT.

f) Electrode diameter might be very important in this type of chemistry like < 25 micrometer etc. But this is not mentioned anywhere.

g) "Since the substrate is generally much larger than the tip, the efficiency of collection, iS/iT, is 1 if no reactions occur during the transfer of tip-generated species to the substrate." Will that be 1 or zero?

3. Significance of this technique lies in various applications of this technique. But authors could discuss how this technique is better or complementary to other techniques as mentioned earlier. The most significant advantage offered by SECM is its capability of probing chemical information of interfacial electrons and ion transfer processes at interfaces. Authors could made this point clear by comparing it with other techniques.

4. Feedback mode/ SG-TC/ SC-TG has their own challenges and every mode cannot be used in each application. Author could explain the limitations of each mode.

5. Figures are well-planned and expressed.

6. Application part is great. However author could mention potential of this technique in a) study of heterogeneous electron transfer on various metal, carbon and semiconductor substrate. ( B. R. Horrocks, M. V. Mirkin, A. J. Bard ''J. Phys. Chem., 1994, 98, 9106 J. V. Macpherson, M. A. Beeston, P. R. Unwin J. Chem. Soc. Faraday Trans., 1995, 91, 899) b) characterization of thin film and membranes (C. Lee, A. J. Bard Anal. Chem., 1990, 62, 1906 C. Lee, J. Kwak, F. C. Anson Anal. Chem.'', 1991, 63, 1501)

Challenges and Limitations
MOFs have can have an extremely high porosity allowing for the adsorption of molecules into the framework. The metals on the framework and functional groups in the pores allow for the possible catalysis of adsorbed molecules. Unfortunately, MOFs are a viable source for catalysis only under mild conditions. Currently MOFs are not able to replace other catalysts like zeolite as inorganic catalyst due to the severe conditions often required. MOFs are mostly used for organic synthesis and enantioselective catalysis due to the favorable conditions for the MOF structure.

Nonchiral Active Sites Within the Homochiral Framework Structures
Kim and coworkers reported the first example of asymmetric catalysis using a homochiral MOF, albeit with a very modest enantioselectivity. Each trinuclear zinc unit in this MOF contains six pyridyl groups, three of which are coordinated to the zinc ions, and two of the remaining three protonated. These exposed pyridine groups showed catalytic activity in the transesterification of ester. When racemic 1-phenyl-2-propanol was used, the ester product exhibited a modest ~8% ee in favor of the S-enantiomer.