Water denitration over titania-supported Pt and Cu by combined photocatalytic and catalytic processes: Implications for hydrogen generation properties in a photocatalytic system
Graphical Abstract
Introduction
Nitrate (NO3¯) can be considered to be one of the most common problems regarding possible contaminants of groundwater. Water-soluble NO3¯ concentrations in the groundwater are rapidly increasing due to excessive fertilization in agriculture, industrial and domestic wastewater. Water pollution with nitrates results in eutrophication and could affect human health through various diseases (blue-baby syndrome, cancer, etc.) [1], [2].
One of the promising technologies capable of reducing NO3¯ to N2 by catalytic hydrogenation of nitrate, have been proposed for the first time by Vorlop et al. [3]. It was reported also [4], [5] the reaction mechanism based on catalytic reduction over bimetallic catalysts using a noble metal (Pd, Pt) and a transition metal (Cu, Sn, In) in the presence of hydrogen as the reductant [6], [7], [8]. Platinum-based catalysts have quite good activity and selectivity for nitrite reduction [9]. To reduce nitrate, it is necessary to activate the precious metal by addition of a promoting second metal [5], [9], [10]. The presence of Cu allows the conversion of nitrate to nitrite, while the further reduction of nitrite to nitrogen or ammonium occurs mainly on precious metal active sites (Pd) [9], [11], [12]. The metals may be present in the form of nanoparticles in order to expose a catalytically more active surface. Loading of TiO2 surface with noble metals such as Pt, Ag, and Au has been investigated from the early times of photocatalysis to increase the photocatalytic activity [13]. Some studies have pointed out the relevance of the structure and geometry of the metal particles in the final mechanism of nitrate reduction [10], [14], [15]. The ability of the (photo) catalytic process to succeed could largely depend on morphology of noble metal deposits (particle size and shape), therefore control of structural properties of metallic nanoparticles is critical to (photo)catalytic performances. Some studies have focused on photochemically produced hydrogen [16] or were concerned with understanding the effect of H2 generation on photoreduction of aqueous nitrate [17], [18].
The present work provides a new approach to the water denitration process and a facile strategy of catalyst preparation for the efficient hydrogen generation. We attempted to improve overall denitration process by using photogenerated charges and in-situ generated hydrogen as reducing agent. This is a very important aspect, because in case of practical application, there is no need for external hydrogen source. The technology becomes widely applicable and the operational costs can be thus reduced significantly. This research aims to tackle nitrate removal from aqueous phase by two approaches: (i) nitrate catalytic reduction by H2 in dark conditions and (ii) nitrate photocatalytic reduction by the in-situ generated solar H2. The present investigation aimed also to get a deeper understanding on the role of surface structures (size and shape of nanoparticles) towards the reduction mechanism and to establish basic principles for an efficient process.
For these purposes, (Pt-Cu)/TiO2 and (Pt-Cu)/TiO2 modified with well-defined Pt nanoparticles were synthesized, characterized using various physicochemical techniques and tested comparatively for nitrate photocatalytic and catalytic reduction reactions. The aim was to favor the selective reduction pathway of nitrate to molecular nitrogen. There are indications that in structure sensitive reactions N-N bond formation rates could be related to preferential orientation of platinum nanocrystal facets [19]. This principle should apply also to nitrate reduction to molecular nitrogen. The idea was to prevent the formation of ammonium ions (NH4+), which is known to be favored by deep hydrogenation of NO3¯ over nanometric sized Pt-Cu nanoparticles.
Section snippets
Catalysts preparation
Two methods of preparation were used: (i) successive impregnation of TiO2 support with metals precursors, and (ii) deposition of well-defined Pt nanoparticles obtained by the preparation procedure described elsewhere [20] onto previously impregnated bimetallic catalyst. In both cases, the calculated copper loading was 0.5 wt%. For comparison purposes, impregnated monometallic catalysts were prepared. The catalysts were prepared with support TiO2 P-25 (Aerosil, Japan, BET surface area 50 m2/g).
Structural property (SEM, TEM and XRD)
SEM images of the synthesized (Pt-Cu)imp/TiO2 and Ptnp-(Pt-Cu)imp/TiO2 are shown in Fig. 2-a and Fig. 2-b, respectively, displaying the morphologies of the calcined catalysts.
The SEM micrograph of (Pt-Cu)imp/TiO2 shows particles with uniform distribution, spherical morphology and slight agglomeration (Fig. 2-a). The SEM micrograph of Ptnp-(Pt-Cu)imp/TiO2 (Fig. 2-b) shows a higher degree of particles agglomeration.
EDAX provides localized elemental information in case of bimetallic nanoparticles.
Conclusions
The point ideas established from the present research are as follows:
- (1)
Overall denitration reaction improvement by combined photocatalytic (responsible for the in-situ H2 generation) and catalytic (accounting for reduction of nitrate by H2) processes, using photogenerated charges and in-situ generated H2 as reducing agent has been achieved.
- (2)
Improved catalytic performance is related to intimate contact between Pt and Cu. Almost 100% nitrate conversion was attained within 150 min over the (Pt-Cu)imp
CRediT authorship contribution statement
Anca Vasile: Conceptualization, Investigation, Writing – original draft. Florica Papa: Resources, Investigation, Supervision. Veronica Bratan: Investigation. Cornel Munteanu: Investigation. Mircea Teodorescu: Investigation. Irina Atkinson: Investigation. Mihai Anastasescu: Investigation. Daisuke Kawamoto: Investigation. Catalin Negrila: Investigation. Cristian D. Ene: Investigation. Tanta Spataru: Investigation. Ioan Balint: Conceptualization, Funding acquisition, Project administration,
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The financial support of the Executive Agency for Higher Education, Research, Development and Innovation Funding (UEFISCDI) Romania, Grants 46 PCCDI/2018 (MALASENT) and PN III-26PTE/2020 (DENOX), is gratefully acknowledged.
References (93)
- et al.
Promoting nitrate reduction kinetics by nanoscale zero valent iron in water via copper salt addition
Chem. Eng. J.
(2016) - et al.
Development of catalysts for a selective nitrate and nitrite removal from drinking water
Catal. Today
(1993) - et al.
Improving the catalytic nitrate reduction
Catal. Today
(2000) - et al.
Catalytic reduction of nitrate and nitrite on Pt-Cu/Al2O3 catalysts in aqueous solution: Role of the interaction between copper and platinum in the reaction
J. Catal.
(2001) - et al.
Hydrogenation of nitrate in water to nitrogen over Pd–Cu supported on active carbon
J. Catal.
(2002) - et al.
Kinetics of the catalytic liquid-phase hydrogenation of aqueous nitrate solutions
Appl. Catal. B Environ.
(1996) - et al.
Catalytic reduction of nitrate on Pt-Cu and Pd-Cu on active carbon using continuous reactor: the effect of copper nanoparticles
Appl. Catal. B Environ.
(2006) - et al.
Influence of metal-support interaction on nitrate hydrogenation over Rh and Rh-Cu nanoparticles dispersed on Al2O3 and TiO2 supports
Arab. J. Chem.
(2017) - et al.
Removal of nitrate and simultaneous hydrogen generation through photocatalytic reforming of glycerol over “in situ” prepared zero-valent nano copper/P25
Appl. Catal. B: Environ.
(2017) - et al.
NO reduction by CH4 over well-structured Pt nanocrystals supported on γ-Al2O3
Appl. Catal. B: Environ.
(2002)
Synthesis of well-defined Pt nanoparticles with controlled morphology in the presence of new types of thermosensitive polymers
Process Saf. Environ.
The effect of pH and zwitterionic buffers on catalytic nitrate reduction by TiO2-supported bimetallic catalyst
Chem. Eng. J.
Copper and platinum doped titania for photocatalytic reduction of carbon dioxide
Appl. Surf. Sci.
Photocatalytic nitrate reduction over Pt–Cu/TiO2 catalysts with benzene as hole scavenger
J. Photochem. Photobiol. A Chem.
Highly active and selective catalytic hydrogenation of p-chloronitrobenzene to p-chloroaniline on Pt@ Cu/TiO2
Appl. Surf. Sci.
Fabrication and enhanced visible-light photocatalytic activity of Pt-deposited TiO2 hollow nanospheres
Chem. Eng. J.
Cu-doped TiO2 systems with improved photocatalytic activity
Appl. Catal. B Environ.
The enhancement of photodegradation efficiency using Pt–TiO2 catalyst
Chemosphere
Exceptional performance of bimetallic Pt1Cu3/TiO2 nanocatalysts for oxidation of gluconic acid and glucose with O2 to glucaric acid
J. Catal.
Pt–TiO2–γ Al2O3 catalyst: I. Dispersion of platinum on alumina-grafted titanium oxide
J. Catal.
Reaction and surface characterization studies of titania-supported Co, Pt and Co/Pt catalysts for the selective oxidation of CO in H2-containing streams
Chem. Eng. J.
SCR of NO by CH4 on Pt/ZrO2–TiO2 sol–gel catalysts
Catal. Today 107–
XPS investigation of strong metal-support interactions on Group IIIA–VA oxides
J. Catal.
Oxygen vacancy model in strong metal-support interaction
J. Catal.
A microcalorimetric study of metal-support interaction in the PtTiO2 system
J. Catal.
Metal–support interaction: Group VIII metals and reducible oxides
Adv. Catal.
Revealing the key oxidative species generated by Pt-loaded metal oxides under dark and light conditions
Appl. Catal. B: Environ.
Preparation, characterization and catalytic behavior of nanostructured mesoporous CuO/Ce0.8Zr0.2O2 catalysts for low-temperature CO oxidation
Appl. Catal. B Environ.
Anomalous metal-support interactions in CuTiO2 catalysts
J. Catal.
TPR, ESR, and XPS study of Cu2+ ions in sol-gel–derived TiO2
J. Solid State Chem.
Hydrogen evolution via glycerol photoreforming over Cu–Pt nanoalloys on TiO2
Appl. Catal. A: Gen.
Catalytic nitrate removal from water, past, present and future perspectives
Appl. Catal. B: Environ.
Titania supported Pd-Cu bimetallic catalyst for the reduction of nitrate in drinking water
Appl. Catal. B: Environ.
Photocatalytic oxidation of butyl acetate in vapor phase on TiO2, Pt/TiO2 and WO3/TiO2 catalysts
J. Catal.
Kinetics of the photocatalytic oxidation of gaseous acetone over platinized titanium dioxide
J. Catal.
Review of surface photovoltage spectra of nano-sized semiconductor and its applications in heterogeneous photocatalysis
Sol. Energy Mater. Sol. Cells
Photocatalytic decolorization of methyl orange in aqueous medium of TiO2 and Ag–TiO2 immobilized on γ-Al2O3
J. Photochem. Photobiol. A
The Modification of Catalytic Properties by Metal-Support Interactions
Stud. Surf. Sci. Catal.
Naphthalene hydrogenation over Pt/TiO2–ZrO2 and the behavior of strong metal–support interaction (SMSI)
Appl. Catal. A: Gen.
Influence of Zn on the characteristics and catalytic behavior of TiO2-supported Pt catalysts
J. Catal.
Some contributions of electron microscopy to the characterisation of the strong metal–support interaction effect
Catal. Today
Comparative study of photocatalytic and non-photocatalytic reduction of nitrates in water
Appl. Catal. A: Gen.
Titanium dioxide photocatalysis
J. Photochem. Photobiol. C.
Fabrication and characterization of Ag–TiO2 multiphase nanocomposite thin films with enhanced photocatalytic activity
Appl. Catal. B: Environ.
Preparation and enhanced photocatalytic activity of Ag@TiO2 core–shell nanocomposite nanowires
J. Hazard. Mater.
Hydrothermal preparation and photocatalytic activity of mesoporous Au–TiO2 nanocomposite microspheres
J. Colloid Interface Sci.
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