Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Black Magic in Gray Titania: Noble-Metal-Free Photocatalytic H2
  Evolution from Hydrogenated Anatase   "Black" TiO2 has gained increasing interest because of its outstanding
properties and promising applications in a wide range of fields. Among the
outstanding features of the material is that certain synthesis processes lead
to the formation of an intrinsic co-catalytic center and thus enable
noble-metal free photocatalytic H2 generation. In this work, we report "grey
TiO2" by an appropriate hydrogenation treatment exhibits excellent
photocatalytic hydrogen. In this case, by the employment of thermally stable
and high-surface-area TiO2 nanoparticles as well as mesoporous particles as the
hydrogenation precursor, the appropriate extent of reduction of TiO2
(coloration) and the formation of Ti3+ is the key for the efficient
noble-metal-free photocatalytic H2 generation. The EPR results reveal that
"grey TiO2" shows stronger Ti3+ feature at g ca. 1.93 than "black TiO2"
contributing to the intrinsic catalytic center for H2 evolution.

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The categories of this paper are: dg-ga
16
The categories of this paper are: stat
28
The categories of this paper are: alg-geom
0
The categories of this paper are: hep-ph
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The categories of this paper are: patt-sol
8
The categories of this paper are: hep-ex
2
The categories of this paper are: math
33
The categories of this paper are: plasm-ph
10
The categories of this paper are: q-bio
7
The categories of this paper are: hep-th
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The categories of this paper are: mtrl-th
31
The categories of this paper are: ao-sci
9
The categories of this paper are: nlin
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The categories of this paper are: bayes-an
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The categories of this paper are: funct-an
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The categories of this paper are: supr-con