NEW PHOTOCATALYTIC APPLICATIONS
Roberto Andreozzia; Ilaria Di Sommab; Raffaele Marottaa; Suellen Satyroa; Danilo Spasianoa
a Dipartimento di Ingegneria Chimica, dei Materiali e della produzione industriale; Università
di Napoli ‘Federico II’; P.le V. Tecchio, 80, 80125, Napoles, Italy
b Istituto di Ricerche sulla Combustione (CNR); P.le V. Tecchio, 80, 80125, Napoles, Italy
The photocatalytic process can be represented as in the diagram, where A is an electron acceptor
(oxidant species) and D is the electron donor (species to be oxidized). The process begins with the
absorption of UV radiation by the catalyst and with the formation of an “electron-hole” pair:
𝒉𝒗
+
−
𝑻𝒊𝑶𝟐
𝒉𝑽𝑩 + 𝒆𝑪𝑩
The high reducing capability of photogenerated electrons allows the reduction of the electron acceptor,
that traditionally is represented by dissolved oxygen. In the latter case, the reaction leads to the formation
of O2•- radicals:
−
•−
𝑶𝟐 + 𝒆𝑪𝑩 → 𝑶𝟐
The positive hole can directly react with dissolved organic substances, water molecules, or OH- ions
adsorbed on the catalyst surface. In particular, the last two reactions generate HO• radicals.
+
−
•
+
+
•
+
𝑯𝑶 + 𝒉𝑽𝑩 → 𝑯𝑶
𝑯𝟐 𝑶 + 𝒉𝑽𝑩 → 𝑯𝑶 + 𝑯
𝑫 + 𝒉𝑽𝑩 → 𝑷
It is well known that the substitution of oxygen with a species capable of reducing, by trapping the electrons in the conducting band, still
enables the oxidation of the organic species present in the solution. Particularly interesting is the case in which oxygen is replaced by a metal
ion (Mn+) dissolved in the solution. The latter reduces to a lower oxidation state by capturing the photo-generated electrons on TiO2, whereas
the organic species oxidizes, through a direct reaction with the positive holes. In some cases, the reduction of the metal results into its
precipitation from the solution thus enabling its separation and recovery.
TiO2 Cu(II)aq
+
BEFORE
…
TiO2
Cu(0)↓
+
Hydrogen production
The oxidation of a sacrificial organic
species
makes
possible
the
continous reduction of cupric ions to
zero-valent
copper
and
the
formation of hydrogen ions. The
latter, in precence of chloride ions,
zero-valent copper, and UV solar
radiation, reduces to generate
hydrogen gas.
V. Lanese, D. Spasiano, R. Marotta, I. Di Somma,
L. Lisi, S. Cimmino, R. Andreozzi;
International Journal of Hydrogen Energy, 2013;
DOI: 10.1016/j.ijhydene.2013.05.101
Selective oxidation
processes
The use of cupric ions instead of
oxygen as electron acceptor allows a
more selective oxidation of an alcohol
(such as benzyl alcohol) into the
respective aldehyde, the formation of
OH radicals being reduced.
Since it is possible to recover the
precipitate copper and reoxidize it by
air bubbling, its role -considering the
whole process - is that of a catalyst.
R. Marotta, D. Spasiano, I. Di Somma, R. Andreozzi and V.
Caprio; Chemical Engineering Journal, 2012, 209, 69–78.
+
+
D
Organic
Species
+
D
Oxidized
Organic
Species
AFTER
IRRADIATION
Treatment of water
from soil remediation
The oxidation of a sacrificial organic
species makes possible the reduction
of metal ions which, in some cases
(as, for example, cupric ions) may
precipitate, thus allowing its
recovery from the solution.