Structure, photoluminescence emissions, and photocatalytic activity of Ag 2 SeO 3 : a joint experimental and theoretical investigation

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Introduction
In recent decades, metallic selenites have attracted great attention because of their different chemical structures and advanced physical properties such as pyroelectricity, ferroelectricity and piezoelectricity, and their important role in the human health specially because selenium is an elemental component of several selenoproteins 1 .[4][5] Some examples of metallic selenite include Pb(SeO3)2 and two modifications of Sn(SeO3)2 (α-and β-) which were synthesized at low-hydrothermal conditions 6 .Crystal structures of SrSeO3 and CaSeO3 and their respective relationships with molybdomeniteand monazite-type compounds were also prepared by hydrothermal methodology 7 .AGa3F6(SeO3)2 (A = Rb, Cs) 8 materials were also studied.Hydrothermal synthesis of Mn(SeO3)2 9 , and orthorhombic phase of β-ZnSeO3 10 which was prepared by treating ZnO with selenous acid solutions were easily obtained.Moreover, orthorhombic isomorphs crystal chemistry of many transition metals of MSeO3 and MTeO3 (M = Mg, Mn, Co, Ni, Cu, and Zn) obtained under high pressure and temperature were considered 11 , as well as bismuth 5,[12][13][14] and indium selenite 15 .Other compounds containing selenium and rare earth elements of different structure type were studied in terms of its solubility, magnetic susceptibility among other properties [16][17][18][19][20][21] .
Silver-contained materials can be considered outstanding compounds for biomedical application because of its low toxicity and bacteriostatic properties, and they can also be used as biomarker and other medical applications.[24] Our research group has demonstrated in other works the successful synthesis, characterization, as well as photocatalytic, photoluminescent and bactericidal applications of silver-based materials such as Ag2WO4 [25][26][27][28][29][30][31][32] , Ag2MoO4 33,34 , Ag2CrO4 35- morphologies due to synthesis methods used which in turn are responsible for different applications.Moreover, high efficient photocatalytic activity of these materials due to different methods 48,49 or use of surfactant 50,51 were recently obtained.
Based on the above considerations, the coupling of Ag and Se in a single building block could give rise to functional activity over others metallic selenites.However, to our best knowledge, there is no work related to the structure, photoluminescence (PL) emissions, and photocatalytic activity of silver selenite Ag2SeO3.Accordingly, in this paper, we report the synthesis of Ag2SeO3 by sonochemistry (SC), ultrasonic probe (UP) coprecipitation (CP), and microwave assisted hydrothermal (MH) methods.These microcrystals were structurally characterized, and first-principles calculations within the framework of density functional theory (DFT) were employed to obtain atomic-level information on the geometry and electronic structure, local bonding, band structure, and density of states (DOS).In addition, the experimental and theoretical structure, vibrational frequency and morphology are compared to rationalize the PL emissions and photocatalytic activity, for first time.

Synthesis
Ag2SeO3 was synthesized by the SC, UP, CP, and MH methods.Silver nitrate (AgNO3), and selenium oxide (SeO2) were purchased from Sigma-Aldrich.In a typical procedure, stoichiometric amounts of Ag + and SeO3 2-solutions were prepared and mixed to form a suspension.In the SC methodology, the suspension was ultrasonicated for 1h at room temperature in a Branson (model 1510) ultrasonic cleaner, and the crystals were collected after turning off the ultrasonic equipment.In the UP methodology, an ultrasonic probe sonicator (Sonics, GEX 750) was used with the probe inserted into the suspension and maintained for 1 hour at room temperature.Along the CP method, the suspension was maintained under stirring at 90 °C for 1h and the precipitated was collected after turning off the stirring.In the MH method, the suspension was transferred to the MH system and maintained at 140 °C for 1h.After that, all the samples were naturally cooled to room temperature, the precipitates were separated by centrifugation, washed with deionized water to remove any remaining ions.Finally, the crystals were collected and then dried in an oven at 60 °C for 12 h.

Characterization
Thermal behavior was studied with a STA (TG/DTA) 409 Netzsch instrument.Samples weight were about 24.5 mg and heating rate was 3 °C/min.The measurement was carried out in O2 (50 mL/min) atmosphere.The materials were structurally characterized by Xray diffraction (XRD) using a D/Max-2000PC Rigaku (Japan) diffractometer with Cu Kα radiation (λ = 1.5406Å) in the 2θ range from 10° to 60° in the normal routine with a scanning velocity of 2°/min and from 5° to 110° with a scanning velocity of 0.2°/min in the Rietveld routine.X-ray photoelectron spectroscopy (XPS) was performed using a ScientaOmicron ESCA+ spectrometer with a high-performance hemispheric analyzer (EA 125) with monochromatic Al Kα (hν = 1486.6eV) radiation as the excitation source.
The operating pressure in the ultrahigh vacuum chamber (UHV) during analysis was 2x10 -9 mbar.Energy steps of 50 and 20 eV were used for the survey and high resolution spectra measurements, respectively.All data analysis was performed using CASA XPS Software (Casa Software Ltd, UK).Micro-Raman spectroscopy was conducted on a Horiba Jobin-Yvon (Japan) spectrometer charge-coupled device detector and argon-ion laser (Melles Griot, United States) operating at 633 nm with a maximum power of 17 mW.Fourier transform infrared (FTIR) spectroscopy was performed at room temperature using a Jasco FT/IR-6200 (Japan) spectrophotometer operated in diffuse reflectance mode (DRIFT).The spectra have a resolution of 4 cm −1 and 32 accumulations per measurement in the range of 400−4000 cm −1 .These measurements were performed on powder mix which was composed of 1% by weight of each sample mixed with 99% by weight of KBr (99%, Sigma-Aldrich).UV-vis diffuse reflectance spectroscopy (UV-vis DRS) were taken using a spectrophotometer (Varian, model Cary 5G) in a diffusereflectance mode.The shapes and sizes of these microcrystals were observed with a field emission scanning electron microscope (FE-SEM) model Inspect F50 (FEI Company, Hillsboro, OR) operated at 5 kV.Photoluminescence (PL) measurements were performed at room temperature with the samples excited by a 355 nm laser (Cobolt/Zouk) focused on a 20 um spot, 50 µW of power.The backscattered luminescence was dispersed by a 20 cm spectrometer with the signal detected by a charged coupled device detector (Andor technologies).

Theoretical methods and model systems
First principle calculations were carried out using the CRYSTAL17 computational package 52 .The crystal structure of Ag2SeO3 was studied by means of DFT calculations at the hybrid exchange-correlation functional level, developed by Lee, Yang and Parr (B3LYP) 53 .It was used extended Gaussian basis sets type 86-pob_TZVP 54 for the Se and O atoms, while the core pseudo-potential SC-doll_1998 55 was chosen for Ag.The accuracy of the Coulomb and exchange integral calculations (TOLINTEG) was controlled by five parameters set to 10 -8 , 10 -8 , 10 -8 , 10 -8 , and 10 -16 , which provide high numerical accuracy.In addition, to provide a more accurate description of the structure crystalline the Mohnkhost-Pack 56 network was defined as 8, featuring eight k-points to describe the region of high symmetry of the crystalline structure.The electronic band structure, DOS and partial DOS projected on atoms and orbitals of Ag2SeO3 were calculated along the appropriate high-symmetry directions of the corresponding irreducible Brillouin zone.
The equilibrium morphology of the crystal of Ag2SeO3 monoclinic (P21/c) was calculated based on the classic Wulff construction 57 , by minimizing the total surface energy (  ) at a fixed volume, providing a simple relationship between the   of the plane (hkl) and its distance in the normal direction from the center of the crystallite 58 .Eight surfaces with index: (011), ( 100), (001), (021), (111), (110), (010) and ( 101) were used to model the ideal morphology and by tuning of the   (ℎ𝑘𝑙) were the complete map of available morphologies is obtained, which were compared with the experimental morphologies obtained from FE-SEM images.  is calculated according to equation: where   is the total energy per repeating cell of the slab,   is the total energy of the perfect crystal per molecular unit,  is the number of bulk units, and A is the surface area per repeating cell of the two sides of the slab.The electronic properties of the surfaces studied, are also are reported.In order to analyze the relation between   and the geometric characteristics of the exposed surfaces, the dangling bond density (  ) was calculated from the number of broken bonds created per unit cell (  ) on a particular surface of area A, according to the expression: 59   =    Eq. 2 To rationalize the pathways connecting the different morphologies shapes predicted, the polyhedron energy (  ) was calculated by summing the contributions of each facet to the morphological shape and the corresponding   values, according to the expression: Eq. 3 where  (ℎ) is the percent contribution of the surface area to the total surface area of the polyhedron, and   (ℎ𝑘𝑙) is the surface energy of the corresponding surface.

Photocatalysis
The photoactivity of the samples obtained was investigated for the degradation of Rhodamine B (RhB) under ultraviolet (UV) irradiation using 6 lamps (Philips TUV, 15 W).50 mg of each catalyst were used, which were added to a beaker containing 50 mL of RhB (1.0 x 10 -5 mol / L).The suspension was placed in an ultrasonic bath (Branson, model 1510; frequency 42 kHz) for 10 minutes and then stirred in the dark for 30 minutes for the absorption-adsorption equilibrium process.The suspension was then exposed to UV light, under constant stirring and maintaining the temperature at 20 °C and at certain times, aliquots were removed, which were centrifuged and the supernatant were monitored through the maximum absorption wavelength of RhB (λmax = 554 nm) using a UV-vis spectrophotometer (V-660, JASCO).

Thermal analysis
TG/DTA measurements were carried out to determine the decomposition temperatures and phase transformations of the Ag2SeO3 samples.The curves are presented in Fig. 1.The results may suggest the following thermal processes which occur under the experimental conditions in O2 atmosphere 60 : Through the DTA curve, at 535 ºC, there was an endothermic process related to the melt of Ag2SeO3, showed by the reaction (1).Reaction (2) represents the decomposition of the Ag2SeO3 between 560 ºC to 930 ºC with a ≈ 40% reduction in sample mass, corroborating the two exothermic processes between 640 ºC and 730 ºC, determined in the DTA curve , except for the Ag2SeO3-UP sample that in this region presented an endothermic process.The endothermic peak at 946 ºC was attributed to the melt of the metallic Ag, as shown by reaction (3) 60,61 .In a nitrogen atmosphere, reaction (2) takes place at a slightly lower temperature (the difference in DTG maxima is ca. 10 °C) than in air, thus corroborating the oxygen evolution 3,60,62 .TG curves of the samples at a temperature close to 1000 ºC, show no stabilization of any silver oxide, which corroborated with the thermodynamic studies at high O2 pressures between 1 to 100 atm by Assal et al. 63 .were evaluated using the general structure analysis system (GSAS) software 66 . Fig Intensity (arb.units) goodness of fit (χ 2 ) and R-value (RBragg), presenting satisfactory values for a quality refinement (see Table 1).Table 1 shows the experimental obtained and theoretical calculated data from Rietveld refinement method, such as lattice parameters, cell volume and the statistical parameters (χ 2 and RBragg).It is possible to confirm by the Rietveld refinement method the absence of additional phase in Ag2SeO3 microcrystal obtained by SC, UP, CP and MH methods, showing that the Rietveld refinement method was performed effectively, corroborating with XRD patterns and ICSD N o 78-388 card 60 , which belongs a monoclinic phase and space group P21/c (Z = 4).
No significant changes were observed among the samples, attesting the structural long-range order of all samples.Table SI-  A representation of the unit cell for the monoclinic Ag2SeO3 structure is presented in Fig. 3.This unit cell was modelled using the visualization for electronic and structural analysis (VESTA) program 67,68 , version 3, and were modelled using lattice parameters and atomic positions obtained from the Rietveld refinement data and from the optimized structure of the theoretical calculation (Ag2SeO3-Theo).Fig. 3 shows the existence of two types of distorted octahedral polyhedrons for the Ag sites, Ag1 and Ag2, and a trigonal pyramid for the Se site.7][78][79][80][81][82] Therefore, all of these results confirm the existence of Ag, Se, and O elements as well as the purity of the samples.

Raman
The structural order in the short range for the Ag2SeO3 samples were determined by Raman spectroscopy.According to factor group analysis, the P21/c structure of Ag2SeO3 presents 72 modes, as stated by the following irreducible representation: Γ = 18Ag + 18Au + 18Bg + 18Bu.Fig. 5 shows the Raman spectra of Ag2SeO3 samples excited at 633 nm.The experimental and calculated vibrational bands of Ag2SeO3 are listed in

FTIR
The FTIR spectra in the 4000-400 cm -1 range of Ag2SeO3 samples are presented in Fig. 6.The characteristic bands of to SeO3 units with C3v point symmetry at 430, 675, 750, and 815 cm -1 can be sensed.The bands at 675 cm -1 , 750 cm -1 , and 815 cm -1 correspond to the symmetric and asymmetric stretching modes of Se-O, while O-Se-O bending mode is observed at 430 cm -1 . 60,83The 900-4000 cm -1 region of the spectra present bands characteristic of CO2 and H2O arising from the room atmosphere and humidity.The symmetrical stretch of carboxylate group can be ascribed to the band identified at 1340 cm -1 .The bending vibration band of molecular H2O appears at 1650 cm -1 .The modes at 2360 cm -1 and 2340 cm -1 and a large mode centered at 3200 cm -1 is

FE-SEM
FE-SEM images of Ag2SeO3 samples are shown in Fig. 7(a-l).All samples present irregular cub-like rods microparticles of different width and length sizes, in the range of 50-800 nm and 1-15μm, respectively.They are agglomerated and present polydisperse size distribution and shape.As shown in the Fig. 7, the particles present smooth surface and well-defined morphology.Figure 7 (c, f, i, and l) also shows the correspondent planes values obtained by DFT calculations which were responsible for the morphologies experimentally observed.
An analysis of the FE-SEM images for the Ag2SeO3-SC microcrystals shown in Fig. 7(a-c) show several elongated rod-like structures, and it is possible to state that microcrystals present a well-defined face-squared and face-rectangular shapes.Fig. 7(df) shows the Ag2SeO3-UP particles of similar morphology, but the average size of these particles is smaller than the Ag2SeO3-UP microcrystals.Drastic reduction on length is observed for the Ag2SeO3-CP as it can observed in Fig. 7(g-i).Finally, the Ag2SeO3-MH crystals observed in Fig. 7(j-l) present rod/cubic morphologies.
The formation of these particles may involve three main steps: self-aggregation, Ostwald ripening (OR) and self-organization.The OR occurs when the medium attain an equilibrium condition among the solubility and precipitation processes.It happens when small particles in suspension redissolve and are deposited into larger ones.Moreover, this process can arise in two steps: a very slow or fast nucleation step, leading to the formation of polydisperse or monodisperse particles, respectively. 88g. 7(a-c) display the Ag2SeO3 crystals obtained when the SC method is used.
The crystals have a rod like flat and elongated shape.The size distribution of the particles, can be related with the crystal sizes that are big enough to be comparable with the ones of the cavitation bubbles. 89Thus, the longer crystallite fragment are observed.Similar qualitative results were obtained for rod shape obtained along UP method as depicted in Fig. 7(d-f).Fig. 7(g-i) show the morphology of the product obtained by the CP method.
It is possible to observe different crystals, some representing a rod like short shape, and the other being nanocrystals formed through crystallographic alignment of the one along a specific crystal surface.The junctions and defects observed in these morphologies, such as twins and staking faults, are a direct evidence of the oriented attachment (OA) growth mechanism. 90,91FE-SEM images presented in Fig. 7(j-l) correspond to sample for Ag2SeO3 crystals obtained by MH and have a hexagonal corner-truncated morphology.
Fig. 9. Band structure for the (011), ( 100), ( 001), ( 021), ( 110), ( 111), ( 010) and ( 101) surfaces of Ag2SeO3.The formation of Ag2SeO3-SC, Ag2SeO3-UP and Ag2SeO3-CP samples comprises two processes which could be related to the OA process: (i) the formation of small Ag2SeO3 nanoparticles as the primary crystal nuclei which exhibited an elongated cube with the exposed ( 100), ( 001) and ( 010) surfaces (A1 shape in Fig. 11); and (ii) the subsequent crystal growth to form single-crystalline Ag2SeO3.Under ultrasound conditions the stabilization of the (101) surface is favored which leads to the flat primary particles (A2 in Fig. 11).The OR process of the primary particles A2 is believed to occur by the coalescence, leading to the formation of A3 crystal (See Fig. 11).The FE-SEM images of Ag2SeO3-SC and Ag2SeO3-UP (Fig. 7(a-c) and 7(d-f) confirm a change in the size and shape of the particles, i.e., the particles initially formed grow preferentially in the (010) direction to form elongated and flat structure).In the case of the Ag2SeO3-CP the interaction between the primary particle units occur through of (001) surface of the A1 shape, as marked by a double arrow in Fig. 11, leading to the formation of a monocrystal.
On the other hand, when the MH radiation is used, the primary crystal nuclei (B1 shape in Fig. 11) is a hexagonal corner-truncated shape with the more exposed ( 011) and ( 111) surfaces and, in minor extent, the exposed ( 021) and ( 010) surfaces.The MH method promotes the appearance of the unstable ( 010) and ( 111) surfaces, derived from the destabilization of ( 100) and ( 110) surfaces with subsequent growth of crystal in the direction (100) to get to render the B2 morphology, and finally, by the stabilization of (021) surface the B3 shape is obtained.The Voigt area G/L function was used for the deconvolution process, resulting in three components at 680 nm, 766, and 876 nm for all samples.An analysis of the results shows that the Ag2SeO3-CP and Ag2SeO3-MH samples have a larger percentage of emission for the 680 nm component.The longer wavelength region of the PL spectra can be related to the presence of vacancy defects and shorter wavelength region is ascribed to intrinsic structural defects.Thus, these samples may present larger numbers of defects, which generate intermediate energy levels between the VB and CB.

Photocatalytic activity
Photocatalytic tests of Ag2SeO3-SC, Ag2SeO3-UP, Ag2SeO3-CP and Ag2SeO3-MH samples were performed under UV light irradiation for photodegradation of RhB.
The aliquots removed at certain times (0, 2, 5, 10, 20, 30, 40 and 60 minutes) were monitored by spectrophotometry using the RhB maximum absorption wavelength (λmax = 554 nm).The absorbance spectra are shown in Fig. 18(a-d) where it is observed that all samples show photocatalytic activity for RhB degradation.
In a similar work, Yang et al. 97     e─h • pairs to act in the photodegradation of RhB, both directly and forming the radical species that can also act on photodegradation.The Ag2SeO3-CP sample showed the lowest photocatalytic activity and the highest PL intensity, confirming that a higher recombination rate can interfere in the photocatalytic activity of the material, since the e─h • pairs are not available to act on the degradation of RhB.The Ag2SeO3-MH and Ag2SeO3-UP samples showed intermediate PL intensities, and consequently their photocatalytic activities were higher than the Ag2SeO3-CP sample and lower than the Ag2SeO3-SC sample.Another point that can explain the higher photocatalytic activity of the Ag2SeO3-SC sample was the change in its particle morphology, which preferably grown in the direction (010), forming an elongated and flat particle, which may have contributed to its photocatalytic response.
In order to understand which radical species are responsible for the degradation process of the RhB dye, radical capture experiments were carried out using tert-butyl alcohol (TBA), ammonium oxalate (AO) and benzoquinone (BQ), respectively, as scavengers of hydroxyl radical (OH*), h • , and superoxide radical (O2'), respectively.These experiments were carried out under the same conditions as the previous tests and using the Ag2SeO3-SC sample, which showed better photocatalytic activity.Fig. 20 (b) shows total inhibition of photodegradation when AO is added, indicating that the h • act directly on the degradation mechanism.When TBA was added, there was a decrease of about 50% in the percentage of degradation, revealing that the OH* species participates to a lesser extent in the degradation process.When adding BQ, there was no change in degradation, revealing that the O2' species is not participating in this mechanism.
In addition to the excellent photocatalytic efficiency, the reuse and stability of the photocatalyst is of utmost importance and was studied using the Ag2SeO3-SC photocatalyst, which showed higher photocatalytic activity.The stability was tested by performing 3 running cycles of RhB photodegradation under UV light irradiation and the results are shown in Fig. 20 (c).Note that from the first to the second cycle the material remains stable and in the third cycle the photocatalytic performance shows a slight decrease.This result can be explained by the photodecomposition and formation of Ag 0 . 99Fig.SI-6 shows the XRD of Ag2SeO3-SC after the photodegradation cycles, and it is possible to observe a peak at 2θ = 38.1°which corresponds to facet (111) of the cubic Ag 0 , confirming the formation of Ag 0 during the photocatalysis process.The Ag 0 formed under the surface of the catalyst prevents the incidence of light, and consequently, reduces the photocatalytic activity of the material. 100The Ag 0 formed under the Ag2SeO3-SC did not significantly affect the photocatalytic activity, being possible the degradation of approximately 97% of RhB in 1 hour of UV light irradiation, showing that the material developed in this study has a good stability, being possible its reuse.The [AgO6] • cluster may also be acting in the production of the OH* radical, which had a relevant participation in the photodegradation process.This radical is generated in the VB of Ag2SeO3-SC sample, as its potential is higher than for the OH*/H2O reaction potential (2.70 eV) 103 , oxidizing H2O by the cluster [AgO6] • , and generating OH* and proton H • , as shown in the following equation: The [SeO3]' cluster present in CB, acting as e, reduces the O2, because the potential of the O2/ O2' reaction (-0.046 eV) 104 is higher than CB of Ag2SeO3-SC sample.
[SeO3]' + O2  O2' + [SeO3] x However, as seen in Fig. 20, the O2' species does not participate effectively in the photodegradation mechanism.Therefore, the whole mechanism occurs through oxidative pathways, by the h • and OH* species.

Conclusions
In summary, Ag2SeO3 monoclinic structure with different morphology has been successfully obtained by four synthesis methods, for the first time.Thermal analysis confirmed the phase stability up to 535 °C.XRD results confirmed the crystallinity of the samples without secondary phases, attesting long-range order of all samples.XPS analysis confirmed that the materials were pure and presented Se 4+ species in all samples.
1 presents the atomic coordinates (x, y, z) for Ag, Se and O atoms obtained by Rietveld refinements and Table SI-2 shows the crystallographic data of Rietveld refinement.It is possible to note a local distortion in the atomic positions (x, y, z) of the atoms, being more prominent in the O positions.Finally, all synthesis methods were efficient to obtain the phase, without amorphous phase.Moreover, all methods enhance the organization of the [SeO3] and [AgO6] clusters within the crystal lattice, preventing the formation of structural defects (stresses and strains), as observed by the higher crystallinity of all the samples.
modeled through of an unreconstructed slab model containing 12, 10, 10, 12, 10, 12, 16 and 16 molecular units, respectively.All possible stoichiometric terminations of each surface were tested, and the optimized surface structure of stable terminations with the lowest value of   are shown in Fig. 8.

Fig. 12 displays
Fig. 12 displays two reaction paths constructed from the calculated   values (TableSI-4).The reaction path A corresponds to a process that goes through a high energy intermediate (A1) until it reaches the final morphologies (A2 and A3) which showed a rather similar stability to the ideal Ag2SeO3 morphology.Along the reaction path B, morphologies with higher   were obtained (B2 and B3).

Fig. 16 shows
Fig.16shows the deconvolution of the PL emissions for the Ag2SeO3 samples.

Fig. 17 Fig. 16 .
Fig.17shows the CIE chromatic diagram and the respective positions of x, and y coordinates of the Ag2SeO3 samples obtained through the PL emission spectra.The (x;y) chromatic coordinates positions are located at Ag2SeO3-SC (0.72;0.28),Ag2SeO3-UP (0.72;0.28),Ag2SeO3-CP (0.71;0.28), and Ag2SeO3-MH (0.71;0.28).All samples present intense emitting colour in the red region, and the (x;y) coordinates are all located near the red edge of diagram, confirming the pureness and brightness of the emitted colour.These results are promising to apply these materials as optical devices.

Fig. 19 (
Fig. 19(a) shows the relative absorbance of each sample as function of irradiation time (t), with A0 being the absorbance at time 0, after the adsorption-desorption period and A being the absorbance at certain times of UV light irradiation.Note that the Ag2SeO3-SC sample degraded practically all RhB in about 1 hour of exposure to UV

Fig. 19 .Fig. 20 (
Fig. 19.Photocatalytic degradation of RhB (1.0×10 −5 mol/L) in the absence and in the presence of different photocatalysts (a) and in log plot for the determination of the rate constant.

Fig. 20 .
Fig. 20.Degradation rate constants (k) of RhB (a), photocatalytic degradation of RhB using Ag2SeO3-SC in the presence of different scavengers under irradiation of UV light (b), and cycling runs for RhB photodegradation over Ag2SeO3-SC under UV light irradiation (c).
Raman and FTIR spectroscopies attested the vibrational modes related to Se-O and Ag-O bonds indicating short-range structural order.FE-SEM images showed rods-, cube-, and faceted-like morphologies due to different methods of synthesis.UV-vis DRS and PL emissions are connected with results of photocatalytic activity, which attested Ag2SeO3-SC as the best performance photocatalyst and Ag2SeO3-CP as the higher PL intensity emission.Based on scavenger trapping experiments, the holes and hydroxyl radical, in minor extent, are the main reactive species during the photodegradation process, and a possible photocatalytic mechanism is proposed.The experimental and theoretical results, supported by first-principles calculations, at the DFT level, were analyzed in terms of the structural and electronic order/disorder effects.The relative stability of the eigth low-index surfaces of Ag2SeO3 were calculated to rationalize the crystal morphologies observed in FE-SEM images (using the Wulff construction) and different energy profiles associated with the transformation processes among morphologies were determined.Present results confirm the Ag2SeO3 based materials are promising photocatalyst with enhanced optical properties.

Table 1 .
Lattice parameters, unit cell volume and statistical parameters of quality obtained through Rietveld refinements of Ag2SeO3 microcrystal obtained by SC, UP, CP and MH methods.

formula Ag2SeO3 Lattice Parameters (Å) Cell volume (Å 3 ) RBragg (%) χ 2 (%) a b c Ag2SeO3-SC
Table SI-3 lists the XPS elements positions and concentration of the area components for Ag, Se and O of the Ag2SeO3 samples.

Table 2 .
Experimental and theoretical values of the Raman and IR vibrational modes of
It is important to note that all considered surfaces are Ag, Se and O terminated, with Ag atoms incompletely coordinated ([  ]  with  = 2, 3, 4, 5) whereas the Se atoms are fully coordinated when compared with the clusters of Se atom in the bulk, i.e., during the slab construction process on each surface, no Se−O bond is broken and the [ 3 ] cluster is maintained.

Table 4 .
Calculated surface energy values (  ), energy band gap (  ), broken bonds • ], [ 6 ]   [ 3 ] clusters are common in both surfaces, however, while (001) surface present [ 4 • 2] clusters, (010) surface present [ 2 • 4] clusters as wellas area smaller than (001) surface.These two characteristics mean that the chemical environment is different on the two surfaces and that the interatomic interactions become more important on the (010) surface, making it more unstable.
related the photocatalytic activity of TiO2 (P25) using RhB dye and UV light irradiation.It was observed that in 30 minutes of irradiation, approximately 90% of the dye is degraded, however the UV lamps used have a power of 500W, about 8 times the power used in our study.The mass of the catalyst and RhB concentration are very close to that used in this work, thus, the Ag2SeO3 samples, highlighting the Ag2SeO3-SC, have very promising photocatalytic activity, degrading all dye in approximately 60 minutes of UV light irradiation, using only 60W of power.