Visible light activation systems

Figure 12 presents the cis-trans relaxation process in the dark (only thermal activation) which is much slower that in the presence of natural visible light. For all the systems, an important percentage of relaxation takes place in the first 24-30 h after this period, the relaxation rate decreases dramatically. As in the case of the natural visible light activated relaxation process, the dark relaxation processes of the azo-polysiloxanes containing adenine and cytosine are very similar. 

The latest systems appear to work under visible light illumination without a noble metal-based H2 and/or O2 catalyst There have been reported photocatalysts such as delafossite CuFe02, without a separate H2 or O2 catalyst, or In/NiAra-oxides coated with NiO, or RUO2 for visible-light activated water-splitting processes. However, all reported water-splitting systems are controversial and require confirmation [3]. 

When composite resins were first introduced, their polymerization involved free radical initiation by a combination of benzoyl peroxide with tertiary amine activator, de-hvered in two different pastes, known respectively as base and catalyst. Contemporary composites are visible light-activated one-paste systems and the principal photoinitiator used is camphorquinone [70,80], It is used in conjunction with a co-initiator, typically an amine [81], This latter compound does not absorb hght, but is necessary to react with the fight-activated camphorquinone molecule to generate free radicals and hence initiate the chain polymerization. 

Watts D C, Amer O, Combe E C (1984) Characteristics of visible-light-activated composite systems. Brit Dent J, 156, 209-215. 

A new hybrid Cu"porphyrin-ZnO system has been recently evaluated as a photocatalyst for the photodegradation of rhodamine B, both under UV-vis and visible light. The system displayed higher photodegradation efficiency than bare ZnO, maintaining the photocatalytic activity over several recycles. This makes Cu°porphyrin-ZnO a promising photocatalyst for future applications. ... 

Another successful development of a photocatalyst/biocatalyst is the integrated system of graphene-based visible-light active photocatalyst and sequentially coupled enzymes, reported by the same authors [104], An isatin derivative... 

Dentures require accurate fit, reasonable chewing efficiency, and lifelike appearance (189). The chewing efficiency of artificial dentures is one-sixth that of natural dentition (190). AcryHc resins are generally used as powder/Hquid formulations for denture base, bone cement, and related appHcations. Polymerization is achieved thermally using initiators photochemicaHy using photoactive chemicals and either uv or visible light irradiation and at ambient temperatures using initiator/activator systems. 

In chemically-cured materials, one example of an initiator/activator system is hydrogen peroxide as initiator, ascorbic acid as activator and cupric sulphate as co-activator. In light-cured materials, camphorquinone is used as a visible-light photochemical initiator, sodium p-toluene-sulphinate as activator and ethyl 4-dimethylaminobenzoate as photoaccelerator. 

Pure Ti02 was recently reported to be active in the disinfection of water contaminated by spores of the type Fusarium solani [142], Bacillus anthracis [143], or Cryptosporidium parvum oocysts [144], or when supported as nanocomposites on zeolite H(i for E. coli deactivation [145], and it found applications in water treatment as a replacement for chlorine. Ag-Ti02 immobilized systems were used for inactivation of bacteria, coupling the visible light response of the system and the strong bactericidal effect of Ag [146]. Silver was deposited on hydroxyapatite to form nanocomposites with a high capacity for bacterial adsorption and inactivation [147], or used for airborne bacterial remediation in indoor air [148],... 

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