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| | If an existing Word - Press code is found vulnerable, Word - Press will immediately issue an update for that. Also, you may want to opt for a more professioanl theme if you are planning on showing your site off to a high volume of potential customers each day. SEO Ultimate - I think this plugin deserves more recognition than it's gotten up till now. They found out all the possible information about bringing up your baby and save money at the same time. Over a million people are using Wordpress to blog and the number of Wordpress users is increasing every day. <br><br>Generally, for my private income-making market websites, I will thoroughly research and discover the leading 10 most worthwhile niches to venture into. If you are a positive thinker businessman then today you have to put your business online. This is the reason for the increased risk of Down Syndrome babies in women over age 35. So if you want to create blogs or have a website for your business or for personal reasons, you can take advantage of free Word - Press installation to get started. Aided by the completely foolproof j - Query color selector, you're able to change the colors of factors of your theme a the click on the screen, with very little previous web site design experience. <br><br>Usually, Wordpress owners selling the ad space on monthly basis and this means a residual income source. Browse through the popular Wordpress theme clubs like the Elegant Themes, Studio Press, Woo - Themes, Rocket Theme, Simple Themes and many more. Use this section to change many formatting elements. These frequent updates have created menace in the task of optimization. Premium vs Customised Word - Press Themes - Premium themes are a lot like customised themes but without the customised price and without the wait. <br><br>Here is more on [http://mmservice.dk/wordpress_backup_947435 wordpress backup] take a look at the webpage. If all else fails, please leave a comment on this post with the issue(s) you're having and help will be on the way. The SEOPressor Word - Press SEO Plugin works by analysing each page and post against your chosen keyword (or keyword phrase) and giving a score, with instructions on how to improve it. This allows for keeping the content editing toolbar in place at all times no matter how far down the page is scrolled. Giant business organizations can bank on enterprise solutions to incorporate latest web technologies such as content management system etc, yet some are looking for economical solutions. Digital digital cameras now function gray-scale configurations which allow expert photographers to catch images only in black and white. <br><br>Someone with a basic knowledge of setting up a website should be able to complete the process in a couple of minutes however even basic users should find they are able to complete the installation in around 20 minutes by following the step by step guide online. It can run as plugin and you can still get to that whole database just in circumstance your webhost does not have a c - Panel area. Must being, it's beneficial because I don't know about you, but loading an old website on a mobile, having to scroll down, up, and sideways' I find links being clicked and bounced around like I'm on a freaking trampoline. Web developers and newbies alike will have the ability to extend your web site and fit other incredible functions with out having to spend more. However, if you're just starting out your blog site or business site, you can still search for an ideal theme for it without breaking your bank account. |
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| '''Photocatalytic water splitting''' is a general term used for the dissociation of [[water]] into its constituent parts, [[hydrogen]] ({{chem|H|2}}) and [[oxygen]] ({{chem|O|2}}), using either artificial or natural [[light]]. [[Hydrogen fuel]] production has gained increased attention as [[Fossil fuel|oil]] and other [[Non-renewable resource|nonrenewable fuels]] become increasingly depleted and expensive. Methods such as photocatalytic water splitting are being investigated to produce hydrogen fuel, which burns cleanly and can be used in a [[hydrogen fuel cell]]. Water splitting holds particular interest since it utilizes water, an inexpensive renewable resource. Photocatalytic water splitting has the simplicity of using a powder in solution and sunlight to produce {{chem|H|2}} and {{chem|O|2}} from water and can provide a clean, renewable energy, without producing greenhouse gases or having many adverse effects on the atmosphere. Theoretically, only solar energy ([[photons]]), water, and a [[catalyst]] ([[photocatalyst]]) are needed.
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| == Concepts ==
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| When {{chem|H|2|O}} is split into {{chem|O|2}} and {{chem|H|2}}, the stoichiometric ratio of its products is 2:1:
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| : <math> 2 \text{ } H_2 O \text{ } \stackrel {\mathrm{photon\,energy}\, > 1.23 eV} {\rightleftharpoons} \text{ } 2 \text{ } H_2 + \text{ } O_2</math>
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| The process of water-splitting is a highly endothermic process (ΔH > 0). Water splitting occurs naturally in [[photosynthesis]] when photon energy is absorbed and converted into the chemical energy through a complex biological pathway. However, production of hydrogen from water requires large amounts of input energy, making it incompatible with existing energy generation. For this reason, most commercially produced hydrogen gas is produced from [[natural gas]].
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| There are several strict requirements for a [[photocatalyst]] to be useful for water splitting. The minimum potential difference (voltage) needed to split water is 1.23V at 0 pH.<ref name="JHEAD">J. Head, J. Turner, “ANALYSIS OF THE WATER-SPLITTING CAPABILITIES OF GALLIUM INDIUM PHOSPHIDE NITRIDE (GaInPN)” U.S. Department of Energy Journal of Undergraduate Research, January 2001, 26-31. [http://www.osti.gov/bridge/purl.cover.jsp?purl=/1051819/ Web link.]</ref> Since the minimum band gap for successful water splitting at pH=0 is 1.23 eV, corresponding to light of 1008 nm, the electrochemical requirements can theoretically reach down into [[infrared light]], albeit with negligible catalytic activity.{{fact|date=April 2012}} These values are true only for a completely reversible reaction at [[standard temperature and pressure]] (1 bar and 25 °C).
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| Theoretically, infrared light has enough energy to split water into hydrogen and oxygen; however, this reaction is kinetically very slow because the wavelength is greater than 380 nm. The potential must be less than 3.0V to make efficient use of the energy present across the full spectrum of sunlight. Water splitting can transfer charges, but not be able to avoid corrosion for long term stability. Defects within crystalline photocatalysts can act as recombination sites, ultimately lowering efficiency.
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| Materials used in photocatalytic water splitting fulfill the band requirements outlined previously and typically have dopants and/or co-catalysts added to optimize their performance. A sample [[semiconductor]] with the proper band structure is [[TiO2|{{chem|TiO|2}}]]. However, due to the relatively positive [[conduction band]] of [[TiO2|{{chem|TiO|2}}]], there is little driving force for {{chem|H|2}} production, so [[TiO2|{{chem|TiO|2}}]] is typically used with a co-catalyst such as [[platinum|Pt]] to increase the rate of {{chem|H|2}} production. It is routine to add co-catalysts to spur {{chem|H|2}} evolution in most photocatalysts due to the conduction band placement. Most semiconductors with suitable band structures to split water absorb mostly [[UV light]]; in order to absorb visible light, it is necessary to narrow the band gap. Since the conduction band is fairly close to the reference potential for {{chem|H|2}} formation, it is preferable to alter the [[valence band]] to move it closer to the potential for
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| {{chem|O|2}} formation, since there is a greater natural [[overpotential]].<ref name="AKUDO">A. Kudo, Y. Miseki, “Heterogeneous photocatalyst materials for water splitting” Chem. Soc. Rev., 38, 253-278 (2009). [http://dx.doi.org/10.1039/b800489g Web link.]</ref>
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| Photocatalysts can suffer from catalyst decay and recombination under operating conditions. Catalyst decay becomes a problem when using a [[sulfide]]-based photocatalyst such as [[Cadmium sulfide|CdS]], as the [[sulfide]] in the catalyst is oxidized to elemental [[sulfur]] at the same potentials used to split water. Thus, [[sulfide]]-based photocatalysts are not viable without sacrificial reagents such as [[sodium sulfide]] to replenish any sulfur lost, which effectively changes the main reaction to one of hydrogen evolution as opposed to water splitting. Recombination of the [[electron-hole pair]]s needed for photocatalysis can occur with any catalyst and is dependent on the defects and surface area of the catalyst; thus, a high degree of crystallinity is required to avoid recombination at the defects.<ref name="AKUDO"/>
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| The conversion of solar energy to hydrogen by means of photocatalysis is one of the most interesting ways to achieve clean and renewable energy systems. However if this process is assisted by photocatalysts suspended directly in water instead of using a photovoltaic and electrolytic system the reaction is in just one step, and can therefore be more efficient.<ref>{{cite journal|last= del Valle |first= F. et al |year= 2009|last2= Álvarez Galván |month= Jun|first2= M. Consuelo|last3= Del Valle|first3= F.|last4= Villoria De La Mano|first4= José A.|last5= Fierro|first5= José L. G. |title= Water Splitting on Semiconductor Catalysts under Visible-Light Irradiation |journal= Chemsuschem |volume= 2 |issue= 6 |pages= 471–485 |publisher= [[CHEMSUSCHEM]] |issn= |pmid= 19536754|pmc= |bibcode= |doi=10.1002/cssc.200900018|ref= }}</ref><ref>{{cite journal|last= del Valle |first= F. et al |year= 2009|last2= Del Valle |month= |first2= F.|last3= Villoria De La Mano|first3= J.A.|last4= Álvarez-Galván|first4= M.C.|last5= Fierro|first5= J.L.G.|title= Photocatalytic water splitting under visible Light: concept and materials requirements |journal= Advances in Chemical Engineering |volume= 36 |issue= |pages= 111–143 |publisher= |issn= |pmid= |pmc= |doi= 10.1016/S0065-2377(09)00404-9 |bibcode= |ref= CONACYT Mexico }}</ref>
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| == Method of evaluation ==
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| Photocatalysts must conform to several key principles in order to be considered effective at water splitting. A key principle is that {{chem|H|2}} and {{chem|O|2}} evolution should occur in a [[stoichiometric]] 2:1 ratio; significant deviation could be due to a flaw in the experimental setup and/or a side reaction, both of which do not indicate a reliable photocatalyst for water splitting. The prime measure of photocatalyst effectiveness is quantum yield (QY), which is:
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| : QY (%) = (Photochemical reaction rate) / (Photon absorption rate) × 100%<ref name="AKUDO"/>
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| This quantity is a reliable determination of how effective a photocatalyst is; however, it can be misleading due to varying experimental conditions. To assist in comparison, the rate of gas evolution can also be used; this method is more problematic on its own because it is not normalized, but it can be useful for a rough comparison and is consistently reported in the literature. Overall, the best photocatalyst has a high quantum yield and gives a high rate of gas evolution.
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| The other important factor for a photocatalyst is the range of light absorbed; though UV-based photocatalysts will perform better per [[photon]] than visible light-based photocatalysts due to the higher photon energy, far more visible light reaches the Earth's surface than UV light. Thus, a less efficient photocatalyst that absorbs visible light may ultimately be more useful than a more efficient photocatalyst absorbing solely light with smaller wavelengths.
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| == Photocatalyst systems ==
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| === {{chem|NaTaO|3}}:La ===
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| {{chem|NaTaO|3}}:La yields the highest water splitting rate of photocatalysts without using sacrificial reagents.<ref name="AKUDO"/> This UV-based photocatalyst was shown to be highly effective with water splitting rates of 9.7 mmol/h and a quantum yield of 56%. The nanostep structure of the material promotes water splitting as edges functioned as {{chem|H|2}} production sites and the grooves functioned as {{chem|O|2}} production sites. Addition of [[Nickel(II) oxide|NiO]] particles as cocatalysts assisted in {{chem|H|2}} production; this step was done by using an impregnation method with an aqueous solution of {{chem|Ni(NO|3)|2}}•6{{chem|H|2|O}} and evaporating the solution in the presence of the photocatalyst. {{chem|NaTaO|3}} has a conduction band higher than that of [[Nickel(II) oxide|NiO]], so photogenerated electrons are more easily transferred to the conduction band of [[Nickel(II) oxide|NiO]] for {{chem|H|2}} evolution.<ref>H. Kato, K.
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| Asakura, A. Kudo, “Highly Efficient Water Splitting into H and O over Lanthanum-Doped NaTaO Photocatalysts with High Crystallinity and Surface Nanostructure” J. Am. Chem. Soc., 125, 3082 (2003).</ref>
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| === {{chem|K|3|Ta|3|B|2|O|12}} ===
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| {{chem|K|3|Ta|3|B|2|O|12}}, another catalyst activated by solely UV light and above, does not have the performance or quantum yield of {{chem|NaTaO|3}}:La. However, it does have the ability to split water without the assistance of cocatalysts and gives a quantum yield of 6.5% along with a water splitting rate of 1.21 mmol/h. This ability is due to the pillared structure of the photocatalyst, which involves {{chem|TaO|6}} pillars connected by {{chem|BO|3}} triangle units. Loading with [[Nickel(II) oxide|NiO]] did not assist the photocatalyst due to the highly active {{chem|H|2}} evolution sites.<ref>T. Kurihara, H. Okutomi, Y. Miseki, H. Kato, A. Kudo, “Highly Efficient Water Splitting over {{chem|K|3|Ta|3|B|2|O|12}}Photocatalyst without Loading Cocatalyst” Chem. Lett., 35, 274 (2006).</ref>
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| === ({{chem|Ga|.82|Zn|.18}})({{chem|N|.82|O|.18}}) ===
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| ({{chem|Ga|.82|Zn|.18}})({{chem|N|.82|O|.18}}) has the highest quantum yield in visible light for visible light-based photocatalysts that do not utilize sacrificial reagents as of October 2008.<ref name="AKUDO"/> The photocatalyst gives a quantum yield of 5.9% along with a water splitting rate of 0.4 mmol/h. Tuning the catalyst was done by increasing [[calcination]] temperatures for the final step in synthesizing the catalyst. Temperatures up to 600 °C helped to reduce the number of defects, though temperatures above 700 °C destroyed the local structure around zinc atoms and was thus undesirable. The treatment ultimately reduced the amount of surface [[zinc|Zn]] and [[oxygen|O]] defects, which normally function as recombination sites, thus limiting photocatalytic activity. The catalyst was then loaded with {{chem|Rh|2-y|Cr|y|O|3}} at a rate of 2.5 wt % [[Rh]] and 2 wt% [[chromium|Cr]] to yield the best performance.<ref>K. Maeda, K. Teramura, K. Domen,
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| “Effect of post-calcination on photocatalytic activity of ({{chem|Ga|1-x|Zn|x}})({{chem|N|1-x|O|x}}) solid solution for overall water splitting under visible light” J. Catal., 254, 198 (2008).</ref>
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| === Pt/{{chem|TiO|2}} ===
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| {{chem|TiO|2}} is the most effective photocatalyst, as it yields both a high quantum number and a high rate of {{chem|H|2}} gas evolution. For example, Pt/TiO2 (anatase phase) is a catalyst used in water splitting. These photocatalysts combine with a thin NaOH aqueous layer to make a solution that can split water into {{chem|H|2}} and {{chem|O|2}}. {{chem|TiO|2}} absorbs only ultraviolet light due to its large band gap(>3.0ev), but outperforms most visible light photocatalysts because it does not photocorrode as easily. Most ceramic materials have large band gaps and thus have stronger covalent bonds than other semiconductors with lower band gaps.
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| === Cobalt based systems ===
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| Photocatalysts based on [[cobalt]] have been reported.<ref>{{cite doi|10.1002/anie.201007987}}</ref> Members are tris([[bipyridine]]) cobalt(II), compounds of cobalt ligated to certain cyclic [[polyamine]]s, and certain [[cobaloxime]]s.
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| In 2014 researchers announced an approach that connected a [[chromophore]] to part of a larger organic ring that surrounded a cobalt atom. The process is less efficient than using a platinum catalyst, cobalt is less expensive, potentially reducing total costs. The process uses one of two supramolecular assemblies based on Co(II)-templated coordination of Ru(bpy)32+ (bpy = 2,2′-bipyridyl) analogues as [[photosensitizer]]s and [[electron donor]]s to a cobaloxime [[macrocycle]]. The Co(II) centres of both assemblies are high spin, in contrast to most previously described cobaloximes. Transient absorption optical spectroscopies include that charge recombination occurs through multiple ligand states present within the photosensitizer modules.<ref>{{cite web|url=http://www.kurzweilai.net/a-less-expensive-way-to-duplicate-the-complicated-steps-of-photosynthesis-in-making-fuel |title=A less-expensive way to duplicate the complicated steps of photosynthesis in making fuel |doi=10.1039/C3CP54420F |publisher=KurzweilAI |date= |accessdate=2014-01-23}}</ref><ref>{{cite doi|10.1039/C3CP54420F}}</ref>
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| === Bismuth ===
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| Bismuth based systems have been demonstrated to have an efficiency of 5% with the advantage of a very simple and cheap catalyst.<ref>{{cite journal|last=Abdi|first=Fatwa F|coauthors=Lihao Han, Arno H. M. Smets, Miro Zeman, Bernard Dam, Roel van de Krol|title=Efficient solar water splitting by enhanced charge separation in a bismuth vanadate-silicon tandem photoelectrode|journal=Nature Communications|date=29 July 2013|doi=10.1038/ncomms3195|url=http://www.nature.com/ncomms/2013/130729/ncomms3195/full/ncomms3195.html|accessdate=5 August 2013}}</ref>
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| == See also ==
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| * [[Artificial photosynthesis]]
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| * [[Photocatalysis]]
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| * [[Photoelectrochemical cell]]
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| == References ==
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| {{reflist|2}}
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| [[Category:Environmental chemistry]]
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| [[Category:Hydrogen production]]
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| [[Category:Photochemistry]]
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