Accepted Manuscript Title: Tungsten oxide – fly ash oxide composites in adsorption and photocatalysis Author: Maria Visa Cristina Bogatu Anca Duta PII: DOI: Reference:

S0304-3894(15)00064-3 http://dx.doi.org/doi:10.1016/j.jhazmat.2015.01.053 HAZMAT 16554

To appear in:

Journal of Hazardous Materials

Received date: Revised date: Accepted date:

25-10-2014 12-1-2015 22-1-2015

Please cite this article as: Maria Visa, Cristina Bogatu, Anca Duta, Tungsten oxide ndash fly ash oxide composites in adsorption and photocatalysis, Journal of Hazardous Materials http://dx.doi.org/10.1016/j.jhazmat.2015.01.053 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

TUNGSTEN OXIDE - FLY ASH OXIDE COMPOSITES IN ADSORPTION AND PHOTOCATALYSIS Maria VISA, Cristina Bogatu*, Anca Duta Transilvania University of Brasov, Dept. Renewable Energy Systems and Recycling, Eroilor 29, 500036 Brasov, Romania,e-mail: [email protected], [email protected]

*corresponding author: [email protected]., tel: +40 268 473113, fax: +40 268 473473

Highlights •

A novel fly ash - WO3 composite was synthesised via mild hydrothermal treatment.

•

Simultaneous dyes and copper adsorption efficiently runs on the composite.

•

In situ tandem systems (TiO2-WO3) supports the high photocatalytic activity.

•

The processes kinetics mainly depends on the dye’s structure and flexibility.

•

Thermodynamics depends on the copper – dye/ copper-dye-substrate interactions.

Abstract A novel composite based on tungsten oxide and fly ash was hydrothermally synthetized to be used as substrate in the advanced treatment of wastewaters with complex load resulted from the textile industry. The proposed treatment consists in one single step process combining photocatalysis and adsorption. The composite’s crystalline structure was investigated by Xray diffraction and FTIR, while atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to analyze the morphology. The adsorption capacity and photocatalytic properties of the material were tested on mono- and multi-pollutants systems containing two dyes (Bemacid Blau - BB and Bemacid Rot - BR) and one heavy metal ionCu2+, and the optimized process conditions were identified. The results indicate better removal efficiencies using the novel composite material in the combined adsorption and photocatalysis, as compared to the separated processes. Dyes removal was significantly enhanced in the photocatalytic process by adding hydrogen peroxide and the mechanism was presented and discussed. The pseudo second order kinetics model best fitted the experimental data, both in the adsorption and in the combined process. The kinetic parameters were calculated and correlated with the properties of the composite substrate.

Keywords: adsorption, photocatalysis, fly-ash, tungsten oxide, wastewater treatment

1. Introduction

The treatment of wastewaters resulted in the textiles industry must include efficient processes for colour bleaching/mineralization along with the removal of other polluting compounds existent in the dyeing and rising baths (heavy metals, surfactants, pHconditioners, whitening agents, etc.). A variety of dyes (azo-, antrachinone, thyazine, metalcomplex dyes) are highly toxic for animals and humans, and affect water transparency reducing light penetration and gas solubility in water [1], thus disturbing the ecosystem. Over 10,000 dyes are currently used in the textile industry and 30% of these are used in an excess amounting about 1000 tones per annum [2]. The loss of reactive dyes during the manufacturing reaches its higher value during the dyeing process because the efficiency of fixation process is about 60-90% [3]. Consequently, the wastewaters exhibit high BOD to COD values (> 2000 mgO2/L) while the discharge limits are much lower (BOD 6.8 and as neutral hydroxide as precipitate, at pH > 7.5. Thus, to avoid copper precipitation the experiments should run in slightly acidic media or close to the neutral pH. In these conditions, the dyes are slightly negatively charged. Thus, high efficiency in both adsorption and photocatalysis are expected by working in weak acidic medium, in good agreement with the literature reports [27-29]. On the other hand, in an industrial process designed for wastewater’s treatment, it is economically feasible to work close to neutral, considering the discharge regulations on pH. Based on all these pre-requisites, the experiments were run at pH=7.0 (the natural pH of the system), when the concurrent protolytic equilibria described by eq (6) and (7) along with the positively charged metal oxides species lead to a nonpolar/slightly polar surface of FAWO3. As consequence the interactions with the pollutants (metal ions and/or dye) are physical based van der Waals attractions. In the multicomponent pollutants solutions, Cu2+– dye interactions can be develop, further influencing the adsorption/photocatalysis rate and mechanisms. A possible reaction is proposed in Fig. 7, involving –SO3- group, but the more complex interactions via the π electrons from the aromatic ring/azo groups or lone pair of electrons from the nitrogen, oxygen or chlorine is also possible.

Fig. 7

The interaction mechanism of Cu2+ with the molecules of BB

3.2.1 Adsorption and photocatalysis from mono-pollutants suspensions of FAWO3

Following the experimental methodology, adsorption and photodegradation experiments were done in the mono-pollutant systems: dye-FAWO3/FAw, WO3 and Cu2+- FAWO3/FAw, WO3. The results are presented in Fig. 8 a, Fig. 8b and Fig 8c. Fig. 8. Efficiency vs. contact time in mono-pollutant suspension: BB, BR on FAw, WO3, FAWO3, in adsorption (a), photodegradation (b) and Cu2+ on FAw, WO3, FAWO3 (c) The dyes adsorption/photodegradation on the investigated substrates depends on two major factors: the dyes structure/flexibility and the substrate characteristics (morphology, heterogeneity, surface charge, distribution of the active sites). As they have quite large molecules, the dyes can follow a multi-center adsorption on the surface, predominantly based on weak physical bonds, involving π electrons from the aromatic rings or the specific functional groups and forming mono- or multi-layers with different degrees of coverage and efficiencies depending on the structure/flexibility. As consequence, the behavior for the two dyes in contact with the adsorbent is different. The adsorption and photodegradation efficiencies on FAWO3 are significantly higher for the BR molecules than for BB in both processes. The differences comes from their structure: BR containing an azo group with a core similar to methylorange leads to a more rigid structure as compared to BB with antrachinone based structure and plenty of σ-bonds allowing the free rotations and thus a higher amount of conformers, with various affinity for the substrate. In the systems with FAWO3, for the BB dye, the equilibrium is reached after 240 min (settled as optimum contact time), while a change in the adsorption mechanism is observed for BR after 240 min (a change of the curve’s slope), corresponding to an activation of the substrate; this can be attribute to the substrate’s saturation with BR molecules, further followed by the second layer formation via interaction of the corresponding π electrons from the aromatic rings or the lone pairs of electrons from the oxygen, nitrogen or chlorine. Similar behavior is observed in dye’s photodegradation. Supplementary information can be obtained and will be discussed based on the process kinetic. In order to outline the properties of the novel composite, parallel adsorption and photodegradation tests were done considering the pollutants interaction with the singlecomponent substrates (WO3 and FAw). Adsorption of the dye molecules onto WO3 shows closer or lower efficiencies as compared to FAWO3, suggesting a similar adsorption mechanism based on van der Waals interactions, with monolayer formation for BB respectively possible multilayer adsorption for BR. The

differences can results from the specific surface values (significantly lower for WO3), but the major factor imposing the process mechanisms is the surface charge (slightly polar for FAWO3, negatively for WO3) and the ionic degree. Under UV irradiation, the rapid and more efficient dye’s degradation is followed by loading/saturation the photocatalyst’s surface at longer contact time (> 180 min) due to the competitive adsorption of the byproducts, resulting in efficiency’s decrease (more evident for BR, less resistant to the oxidation process). In the mono - pollutant system containing copper ions, the good efficiencies registered for FAWO3, and even for WO3 and the considerable lower values for FAw, can be explained considering the surface charge (Table 3) respectively considering the interactions pollutantssubstrates (stronger on the negatively charged WO3 surface at the working pH), the specific surface and the number of active sites (higher for FAWO3 allowing multiple interaction possibilities with the copper ions). Thus, in copper removal using FAWO3, a key role is played by the specific surface; additionally, the high efficiencies can be obtained due the possible interaction of the copper ions with the WO3 embedded in the FA matrix that can generate local negatively charged regions according to equations (6) or (9). FAw with a large heterogeneity in the active sites distribution and the positively charged surface (in the experimental condition, pH0.5 g) results in thicker layers which may act as a barrier for the UV light, the real contact surface with the dye remaining almost the same. Also, the turbidity of the dispersion increases and reduces the amount of radiation reaching the substrate. However, this static photocatalytic procedure can be very easily up-scaled. Therefore, for photocatalytic test the optimum mixing ration was fixed at 0.5 g of substrate for 50 mL of pollutants solution for both dyes. For correct comparison criteria, the same ratio was also fixed for further adsorption tests. Preliminary tests on the photocatalytic activity of FAWO3 composite on BB dye (the most resistant dye in the removal process) have showed efficiencies of 0.5% for 1h VIS irradiation, lower than the corresponding efficiencies obtained under UV irradiation (0.95%). This also showed the need for extended process durations, and experiments were done up to 240 min.

The effect of the H2O2 addition on the dye’s removal

In the photocatalytic process, an electron-hole pair is formed under irradiation with a suitable energy (UV or VIS with value equal or higher than the semiconductor band gap), eq. (11); the holes are further involved in the hydroxyl radicals formation, eq. (12). Photocatalyst + hν → e- (Photocatalyst) + h+( Photocatalyst) (11) h+ + H2O → HO• + H+ (12) These are powerful oxidizing species, able to degrade the dyes molecules (adsorbed on the catalyst or in solution, near the photocatalyst surface) to smaller fragments less colored, equations (13 - 14), probably with similar dimensions /charges which can be further adsorbed onto the active sites of substrate or can be further degraded up to mineralization [26- 29, 33, 34]: HO• + dye → oxidation products (13) HO• + oxidation products → CO2 + H2O + mineralization products (14) The addition of hydrogen peroxide follows a well-known mechanism to enhance the dyes degradation by increasing the rate of hydroxyl generation, eq. (15) and by acting as electron acceptor for the photogenerated electron in the conduction band (CB) thus promoting charge separation, eq.(16) [27, 35, 36]: H2O2 + O2-• → HO- + HO• +O2 (16) H2O2 +e-(CB) → HO- + HO• (15) H2O2 +hν → HO• + HO• (17) The last reaction, eq. (17), requires irradiation with wavelength less than 250nm, thus is not likely to occur in the experimental conditions. In the absence or with small amounts of these reactive species (hydrogen peroxide of oxygen), in the vicinity of the photocatalyst surface, the electron-hole recombination is fast and the corresponding absorbed energy will dissipate as heat. However, excess of hydrogen peroxide is likely to support the hydrogen peroxide decomposition into water and oxygen. Thus, the dosage of the hydrogen peroxide is important in the photocatalysis effect. Many

papers [27, 28, 35, 36] discuss the effect of hydrogen peroxide in the treatment of the wastewaters containing dyes, focusing on the optimal H2O2 amount, the pH influence, but also considering the costs for the industrial photocatalytic process. Therefore, the influence of the hydrogen peroxide on BB and BR removal (photocatalysis and adsorption) using the new composite FAWO3 material were further developed. For comparison reasons, parallel experiments using WO3 were developed, in the same types of processes. All tests were done in the using the optimized condition (contact time, substrate mass: solution ratio, initial dye’s concentration), at the natural pH and the efficiencies are presented in Fig. 10a and Fig 10b.

Fig. 10 The effect of the H2O2 on the BB and BR removal in adsorption and photocatalysis on: (a) FAWO3; (b) WO3 By increasing the H2O2 concentration, the degradation efficiency gradually increases, due to the hydroxyls formation according to equations (15-17). If H2O2 is overdosed, equilibrium is reached on FAWO3, while a decrease of the removal efficiency is registered on WO3. Similar effects were reported in the photocatalysis of dyes or other organic compounds degradations (e.g. methylene blue, methyl orange, Reactive orange 4, chlorinated aniline, pesticides, etc) [27, 35-38]. This phenomenon results from the formation of hyperoxyl radicals (H2O•) less reactive than the hydroxyl, hydrogen peroxide behaving as scavenger for the HO• according to eqs. (18) and (19): H2O2 + HO• → H2O + HO2• (18) HO2• + HO• → H2O +O2 (19) Additionally, excess H2O2 can react with the oxidative holes (h+, from the valence band-VB) on the catalyst surface with oxygen formation, inhibiting the HO• generation and resulting in a decrease of the overall bleaching efficiency, eq.(20): H2O2 + 2h+VB → O2 + 2H+ (20) Based on these results, an optimum volume of the hydrogen peroxide of 0.12mL/50 mL solution of BB and 0.05 mL/50 mL solution of BR was chosen. These values and the higher efficiencies recorded for BR confirms the higher reactivity of the BR molecules in the photodegradation process.

The effect of hydrogen peroxide addition in the photocatalysis must be related to the solution pH. A significant reduction effect on dyes degradation was observed and reported mainly in alkaline/strong alkaline media [27, 36, 39]. Factors that can be involved in this behavior are: the instability of H2O2 in alkaline medium, leading to self-decomposition with oxygen formation, eqs. (21), or the formation of the hydroxyperoxy anion, HO2- (the conjugate base of H2O2), eq. (22) that can consume the hydroxyl in reactions as eq. (23): H2O2 →H2O +1/2O2 (21) H2O2 → HO2- + H+ (22) HO2- + HO• → H2O + O2-• (23) In the experiments run at natural pH, close to neutral, the positive effect of hydrogen peroxide on the dye’s degradation should not be affected. A comparative view of the new substrate vs. WO3, outlining the effect of H2O2 addition during adsorption and photocatalysis is presented in Fig. 11. Fig. 11 The influence of the H2O2 addition on the removal process of BB and BR dyes A significant increase in the adsorption efficiency of dye’s molecules onto the new composite substrate is observed when hydrogen peroxide is added in the system. This can be related to an activation effect of the surface in the presence of hydroxyl radicals that can results in new active sites available for the dye’s molecule. Surprisingly, much better photocatalytic efficiency was obtained in the case of BB, on the new substrate comparing to WO3, a typical photocatalyst, while slightly lower values result for the BR dye. The difference results from the dye structure inducing a higher flexibility and reactivity for BR, that can be efficiently removed using WO3 (single) photocatalyst. The photocatalytic activity of FAWO3 mainly results from the WO3 content, but the difference can come from the contribution of other oxide like TiO2, Fe2O3 and MnO2 that can become active under UV illumination, possibly forming in situ tandem systems (e.g. TiO2-WO3) that can directly participate in the process, forming electron –holes pair and oxidizing hydroxyl groups, or can serve as adsorbent for the oxidation by-products; these systems can be more efficient for the most resistant pollutants. Future studies will investigate the application of this system for photocatalytic materials based on fly ash.

3.2.2 Heavy metals and dyes adsorption/photodegradation from multi-pollutant solutions Investigations in multi-pollutants systems, simulating the composition of the wastewaters from textile industry, are of importance as primary step in upscaling the process at industrial level. In the multi-pollutants systems interactions can occur, governed by the pH and the dye(s) – Cu2+ interactions, as Fig. 7 showed. The efficiencies obtained for the BB or BR dye and copper removal are presented in Fig. 12a-12d, for the novel composite and respectively for the single components of the substrate (FAw and WO3). Fig. 12. Efficiency of BB (a) and BR (c) and copper (b, d), removal from the systems: (Cu2++BB, Cu2++BR) in adsorption and simultaneously adsorption and photodegradation

A fast adsorption of the BB molecules is observed for all substrates (FAw, WO3 and FAWO3) and the equilibrium is reached after 30…60 min.; the presence of WO3 in the FAWO3 structure does not significantly influence the adsorption in the beginning (≈ 30 min), suggesting that the first blocked are the fly ash active sites and only later the available active sites from WO3 embedded in the FA structure are used (Fig. 12 a). For Cu2+, the adsorption equilibrium is reached after 90 min, and WO3 generates new active sites for the copper ions, leading to higher efficiencies. A cumulative effect of FAw and WO3 in the copper ions adsorption is observed (Fig. 12.b). In the case of BB dye, an activation effect of the copper ions on adsorption compared to the mono-pollutant solution is observed (Fig. 8a and Fig. 12 a). A similar behavior was reported for the system cadmium - anionic surfactant, sodium dodecylbenzene sulphonate [15]. This can be the results of the Cu-dye interaction in the solution (according to Fig. 6), reducing the molecule flexibility, followed by the high volume aggregate adsorption with high coverage degree. As consequence, the real concentration of the remaining free dye in the solution becomes lower, leading to an apparent higher efficiency in adsorption and/or bleaching. In the systems containing BR and copper ions, higher adsorption efficiencies are recorded for both FAw and FAWO3, in good agreement with the structure and reactivity/ affinity towards the substrates. Copper activation effect on the BR adsorption is also observed (Fig. 8b and Fig. 12c). The behavior of the two systems in contact with FAw is different. There is a competition between the pollutants adsorption: copper ions are preferential absorbed in the system with BB, while BR adsorption is more favored in the BR+Cu2+ system. This can be correlated with the dyes structure: the more flexible is the dye the more difficult it is to remove. Thus, the

adsorbed BB molecules can act as a complexion agent, functioning as electron donor for copper ions, thus increasing the substrate’s affinity for the metal ions [18], supporting copper adsorption. Comparatively, the adsorption of BR is faster than copper adsorption, BR rapidly blocking the FAw pores distributed on the positively charged surface. Additional information is presented in the section discussing the processes kinetics (section 3.2.3). As expected, there is no significant influence of the irradiation duration, and very good removal efficiencies are recorded after 60 min for the dye and 90 min for metal’s ion. These values are also convenient from technological point of view. Better results are obtained compared to the untreated substrate (FAw) for both BB dye and copper ions (in both systems), in agreement with the SEM/AFM results that prove that the novel composite has a more uniform surface in terms of pore dimensions and distributions. In the BR + Cu2+ system, very good efficiencies - with similar values for FAw and FAWO3, are obtained. Under UV irradiation and stirring, the removal efficiencies considerably increase suggesting a fast process of dye’s photodegradation in the beginning, leaving a high number of available active sites for pollutants (dye or copper) or for the corresponding by-products. A slight improvement in the copper removal efficiency is also obtained (Fig. 12 b, Fig. 12d). As expected, BR molecules are removed in the simultaneous adsorption –photodegradation process with higher efficiencies (compared to BB) when using FAWO3. Similar to the mono -pollutant suspensions, the decrease in the dye removal efficiencies for longer contact durations (t > 60 min) on the WO3 based substrates corresponds to the WO3 surface saturation. The use of FAw as substrate for dyes removal under UV light irradiation leads to higher efficiencies than for FAWO3 but this is mainly the consequence of the surface charge (positive in the experimental condition) and ionic degree of FAw, that allows stronger electrostatic interactions with the dye’s molecules, adsorption being the main process. Moreover a higher affinity of the photocatalysis products for FAWO3, is also possible, favoring their adsorption, thus blocking the available sites for dye’s removal. A significant decrease in the efficiencies of BB dye photodegradation under visible light in multipollutants systems onto FAWO3 was registered comparing to UV irradiation (64.78% efficiency). The preliminary tests for 1 h photocatalysis process (under mixing) lead to 29.5 % efficiencies, result that can be interesting for possible practical applications. These data are good as previous studies on dyes (BB, BR) removal via adsorption, photocatalysis or simultaneous processes showed that by using TiO2 photocatalyst a

maximum efficiency of 50% was obtained after 6h UV irradiation, [33]; additionally, using mixtures of FAw and TiO2 as substrates for BB, BR dyes removal from multicomponent systems in simultaneously adsorption and photocatalysis process, efficiencies less than 40% have been obtained, [5]. These values are comparable or even lower than the corresponding values obtained with FAWO3, (Fig. 8, Fig.12), indicating potential applications of this material in the wastewater treatment. 3.2.3 Uptake kinetics for copper ions and dye In order to have complete information on the adsorption and photocatalysis processes, kinetics studies were developed for dyes in mono-pollutant systems and for multicomponent suspension containing the most resistant dye, BB. The mostly used model for describing the adsorption process is the pseudo-second order kinetic [40] that assumes comparable concentrations of the surface active sites and of the pollutants molecules/species.

t 1 t = + qt k 2 qe2 qe (24) where: k2 is the pseudo second-order rate constant (g mg-1 min-1), and qe is the equilibrium adsorption capacity. The adsorption capacity at the pre-set moments, qt, for the given solution volume, V, and amount of substrate, ms, were evaluated from the initial ( concentration ( qt =

t cCu 2+ / BB

i cCu 2+ / BB

) and momentary

) of pollutant using eq. (25)

i t (cCu − cCu ) ⋅V 2+ 2+ / BB / BB

ms (25)

For the photocatalysis process, the Langmuir-Hinshelwood mechanism simplified for low concentrations as a pseudo first order kinetics was tested, eq. (26):

ln c/co= kt (26)

The kinetic parameters and the correlation coefficients calculated from the linear form of the kinetic laws are presented in Table 3 and the kinetic plots are given in Fig.12.

Table 5 The kinetic parameters for dye and copper ions removal in adsorption and photocatalysis Fig. 13 Pseudo-second order kinetic plot for adsorption of (a) BB (k= 0.0125 g/mg min, qe = 1.222 mg/g) and (b) BR (k=0.242 g/mg min, qe =2.404 mg/g) on FAWO3; t=0….360 min In the mono-pollutant dye systems, the pseudo-second order kinetic model is not valid for the entire tested adsorption duration (Fig. 12); for both dyes, the linearization with good correlations coefficients was possible only for limited time intervals indicating that more complex mechanisms are likely outside this range. Similar results were previously obtained for dyes removal from complex loaded wastewaters resulted from textiles dyeing industry [5]. The adsorption process (rate and efficiency) is conditioned (especially in the first moments) by the number of pollutants molecules that reach the substrate/active sites; the diffusion of dye molecules from solutions to the substrate surface represents the limiting step in the process. The flexibility, but also the molecule’s dimension influences the diffusion, and leads to a lower diffusion rate for the larger BB molecules. Once a sufficient number of the dye molecules have reached the substrate, the process is well described by the pseudo second order kinetic model. The adsorption is faster for BR, the active sites are more rapidly blocked and the substrate’s saturation results, while for BB no saturation is attained (Fig.13a, 13b). The values of the kinetic parameters confirm also the slower adsorption of the more flexible BB molecules comparing to the more rigid BR dye. The kinetic facts are in agreement with the efficiency vs. time results (Fig. 7): the more flexible the dye is, the slower is the adsorption process and the less is the adsorption efficiency. In the multi-pollutants systems, the experimental data fit very well the pseudo-second order kinetic model for both pollutants and processes. The reaction rate constants are significantly higher for the dye as compared to the copper ions in both processes: adsorption and combined A+F (under stirring), and can be related to the higher mobility and affinity of this pollutant for the substrate. The kinetic parameters indicate a faster dye adsorption, followed by a slower copper adsorption occupying the remaining FAWO3 active sites; copper interaction with the π electrons from the aromatic ring or the functional groups with the adsorbed BB molecules or formation of complexes Cu2+-BB with lower mobility but with a good coverage degree in the adsorption must be also considered. These facts explain the high value of the

equilibrium/maximum adsorption capacity and lower reaction rate for copper and are in agreement with the efficiency’s vs. time data. During UV illumination under stirring, the BB molecules are removed from the substrate in a rapid photo-bleaching process (high k2), leaving more active sites for pollutants’ (BB, Cu2+) or by-products adsorption. Consequently, the qe values slightly decrease for BB (due to the partially degradation) and increase for copper ions. The process respects the pseudo-second order kinetic both for the dye and metal ions, suggesting that the limiting step in the mechanism is the pollutants adsorption. The rapid dye photodegradation is also proved by the validity of Langmuir - Hinshelwood mechanism (R2 = 0,993) in the multi-pollutants system, for short contact durations (15…60 min). Based on the kinetic data, it can be conclude that the limiting step is the copper removal, imposing the technological parameters (e.g. a contact time of 90 min).

Conclusions A new composite substrate, based on fly ash and tungsten trioxide with zeolite type structure was hydrothermally synthesized for the removal of copper and dyes from the textile industry wastewaters. The interactions among the components and with the new compounds formed during synthesis were proved based on the XRD, AFM/SEM and FTIR investigations. The incorporation of the nano-sized WO3 into the micro structure of FAw lead to more uniform aggregates, with regular surface distribution of the pore, efficient in dyes and copper removal from multi-component pollutants suspensions. The efficiencies in the adsorption and photocatalysis and the kinetic data/kinetic parameters in mono- and multi-pollutants systems were comparatively discussed and correlated with the dyes structure and flexibility and copper – dye/ copper-dye-substrate interactions. Simultaneous adsorption and photocatalysis were developed on the new composite substrate, with removal efficiencies up to 70% for the BB dye and over 90% for the copper ions. The adsorption and photocatalytic properties were comparatively discussed for the novel composite and for the single components. Pseudo-second order kinetic model described well both adsorption and combined adsorption-photo-catalysis processes in the multi-pollutants systems, proving that adsorption is the limiting step in the mechanism. The influence of hydrogen peroxide addition on both processes: adsorption and photocatalysis was investigated and discussed. The better photocatalytic activity of FAWO3/H2O2 system comparing to WO3, a typical photo catalyst, indicate that the new material is a competitive

substrate in terms of cost and efficiency that can be successfully used for dyes and heavy metals removal.

Acknowledgments:

This work was supported by the grant PNII-RU-TE-2012-3-0177/2013, financed by Romanian National Authority for Scientific Research, CNCS – UEFISCDI.

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40. Ho Y.S., McKay G.J., Comparative sorption kinetic studies of dye and aromatic compounds onto fly ash, J. Environ. Sci. Health 34 (1999) 1179-1204 List of figure caption

Fig. 1 Chemical structure of the dyes Fig. 2 X-ray difractogram of (A) FAw; (B) FAWO3; (C) WO3 Fig. 3 AFM topography and pore distribution before adsorption/photocatalysis for: a) FAw (average roughness: 91nm); b)WO3 (average roughness: 36 nm); c) FAWO3 (average roughness: 46 nm) Fig. 4 SEM images for: a) FAw; b) FAWO3 as synthesized Fig. 5 FT-IR spectra of the FAw and FAWO3 before adsorption/photocatalysis Fig. 6 UV-Vis reflectance spectra of FAw, WO3 and FAWO3 before adsorption/photocatalysis Fig. 7 The interaction mechanism of Cu2+ with the molecules of BB Fig. 8. Efficiency vs. contact time in mono-pollutant suspension: BB, BR on FAw, WO3, FAWO3, in adsorption (a), photodegradation (b) and Cu2+ on FAw, WO3, FAWO3 (c) Fig. 9 Dyes removal efficiency vs mass of substrate in mono-pollutant suspension of BB/FAWO3 and BR/ FAWO3 in adsorption (A) and photocatalysis (F) processes Fig. 10 The effect of the H2O2 on the BB and BR removal in adsorption and photocatalysis on: (a) FAWO3; (b) WO3 Fig. 11 The influence of the H2O2 addition on the removal process of BB and BR dyes Fig. 12. Efficiency of BB (a) and BR (c) and copper (b, d), removal from the systems: (Cu2++BB, Cu2++BR) in adsorption and simultaneously adsorption and photodegradation Fig. 13 Pseudo-second order kinetic plot for adsorption of (a) BB (k= 0.0125 g/mg min, qe = 1.222 mg/g) and (b) BR (k=0.242 g/mg min, qe =2.404 mg/g) on FAWO3; t=0….360 min

List of Table Caption Table 1 Fly ash composition Table 2 Surface properties of FAw, WO3 and FAWO3. Table 3 The surface charge dependence on pH for FAWO3

Table 4 The PZC’s values [30] and character of the major oxide’s component of fly ash adsorbent Table 5 The kinetic parameters for dye and copper ions removal in adsorption and photocatalysis

Table 1 Fly ash composition

SiO2

Al2O3

Fe2O3

CaO

53.32

22.05

8.97

5.24

Major oxides [%] MgO K2O 2.44

2.66

Na2O

TiO2

MnO

LOI

0.63

1.07

0.08

1.58

Trace elements [ppm] Ba

Cu

Zr

Sn

Pb

As

Ni

Zn

Cr

V

Mn

Co

Ti

700

60

100

3

35

100

55

160

100

115

800

12

>3000

Table 2 Surface properties of FAw, WO3 and FAWO3. Sample

BET surface area

Total pore volume

Average pore

[m2/g]

[cm3/g]

diameter [nm]

FAw

10.33

0.06

27.2

WO3

8.606

0.057

26.76

FAWO3

31.189

0.098

12.67

Table 3 The surface charge dependence on pH for FAWO3

pH

………4… 5.33 ......6..7 .................7.91 .................14

WO3

+++++------

-----

FAw

+ + + + + + + + + + ++ + + + + ++ + + + + +

FAWO3 + + + + + ++ + + +

Dissolution

0 00 00 00 000 0

Dissolution ---------- - - - - - - -

Nonpolar/weak polar

Table 4 The PZC’s values [30] and character of the major oxide’s component of fly ash adsorbent Oxide

SiO2

Al2O3

Fe2O3

SiO2-Al2O3

FAWO3

PZC

2.4…6.6

8.5…9.3

7.5….8.8

4….4.6

5.33 and 7.91

Ionic-covalent

Ionic

Covalent; ionic- Mixed

Predominant Covalent bonds

covalent

Table 5 The kinetic parameters for dye and copper ions removal in adsorption and photocatalysis

Parameter

BR

Process

BB

BB/(BB+Cu2+

Cu2+/(BB+Cu2+)

) Time [min]

k2

A

[g/mg·min

A+F

60..300

0..240

120…360

0…240

0…240

0.2423

0.210

0.0158

0.0192

0.0029

-

-

-

1.703

0.0027

2.404

2.316

0.972

1.475

28.089

-

-

-

1.194

32.051

0.9704

0.9736

0.9826

0.9474

0.9988

-

-

-

0.9954

0.9996

] qe

A

[g/mg·g]

A+F

R2

A A+F

FIG 10a .

FIG 10b .

FIG 11 .

FIG 11_BLACK-WHITE .

FIG 3a .

FIG 3a_black _white .

FIG 3b .

FIG 3b_black _white .

FIG 3c .

FIG 3c_black _white .

FIG 4a .

FIG 4b .

FIG 5 .

FIG 5_black-white .

FIG 8b .

FIG 8c .

FIG1 .

FIG12a .

FIG12b .

FIG12c .

FIG12d .

FIG13a .

FIG13b .

FIG2 .

FIG2_black-white .

FIG6 .

FIG7 .

FIG8a .

FIG9 .