DEVELOPMENT OF GREEN CONCRETE BEAD COATED WITH METAL DOPED NANOTITANIA AND SILICA CONJUGATE AS PHOTOCATALYST AND USE THEREOF

Abstract

The present invention deals with spherical or rod- shaped photocatalyst which comprises green concrete beads (GCBs) with a surface coating of iron-doped nanotitania conjugated silica particles. The preparation method comprises of two steps: (i) the synthesis of iron doped nanophotocatalyst (Fe-nanoTiO2) was conjugated with SiO2 (ii) the preparation of coated GCB by depositing of Fe-nanoTiO2/SiO2 on the surface of GCB via controlled binding of epoxy resin. The preparation of GCB was carried out by mixing of convectional cement with partial replacement of coal fly ash (CFA) derived zeolite. The present invention relates to the photocatalytic degradation of pollutants such as congo red, crystal violet, methylene blue, 4-nitrophenol and chlorpyrifos. The invention also relates with the antibacterial potential of photocatalyst coated GCBs.

Specification

Description:FIELD OF THE INVENTION: -
The present invention relates to the technical field of a "Concrete Supported Photocatalyst (CSP)" for the remediation of multiple aquatic pollutants wherein green concrete bead (GCB) supported iron-doped nanotitania and silica conjugate was used as photocatalyst. The disclosure also relates to the method of GCB preparation, wherein Portland cement was partially replaced with coal fly ash-derived zeolite. The present disclosure also relates to the method of the preparation of stable binding of the photocatalyst i.e. iron-doped nanotitania and silica conjugate, onto the surface of GCB by using epoxy resin.
BACKGROUND OF INVENTION: -
Advance oxidation photocatalytic methods are efficient ways for treating wastewater containing various aquatic pollutants such as dyes, phenols, pesticides etc. The development of noble photocatalyst with enhanced catalytic capabilities, high stability, and increased surface area has been the topic of numerous research in last decade. However, after the treatment process, handling the suspended nano-photocatalyst is a major challenge. Upscaling of suspended photocatalytic systems is not commercially feasible due to the lack of appropriate photocatalyst separation methods and the toxicity of nanoparticles [1]. The idea of immobilising photocatalysts on an appropriate solid substrate may help to get rid of the problems while encouraging the reuse and recycling of photocatalysts. The immobilisation of nanoparticles on support substrates such as sand [2], stone [3], glass [4], clay [5], wood [6], concrete [7] etc. has been reported recently in numerous investigations. Although the effectiveness of nano-photocatalyst in degrading organic pollutants has been demonstrated, separating them from the solution is a difficult task. Contrary to that, efficient and speedy post-treatment separation of nanophotocatalysts can be either permanently kept in the photocatalytic reactor (such as glass plates, stainless steel, metal wire mesh, metal foams, etc.), or readily removed by physical separation post-treatment separation methods when attached to supports like quartz sand, calcium alginate hydrogel beads, black volcanic ashes, etc.
Early in the 1990s, photocatalytic materials were first used with cementitious materials. The commonly used immobilization methods includes dip-coating, electrophoretic method, sol-gel, solvothermal, spray pyrolysis, and cold plasma discharge [8]. According to the studies, the immobilized photocatalysts demonstrated enhanced catalytic activity, speeding up the breakdown of organic contaminants.
TiO2 has been so far reported as a highly efficient photocatalyst due to its potential absorption capability of UV radiation, low cost, exceptional photo-corrosion stability, non-toxicity, and easy availability [8].
Due to the wide energy band gap of TiO2, doping of elements is usually recommended to reduce its energy band gap. A reduced energy band gap speeds up the photocatalytic degradation of pollutants even under visible light or sunlight. Thus, the process can be made energy efficient and sustainable. Doping of metals and non-metals has been considered as one of the best ways to reduce energy band gap. Preferably, transition metals are selected due to half-filled 'd' orbitals [9]. Their doping into TiO2 generates new energy level near the conduction band. To shift the energy band gap TiO2 to the visible light range, doping of oxides of transition metals such as Fe, Zn, Cu, Ni, and V were studied by many groups [10].
According to the above literature, in our work, we selected Iron as the dopant for nano TiO2 because iron atoms easily settled down in the lattice of TiO2 and acted as a charge-trapping centre. It can also promote photo-Fenton reaction to produce free radicals, leading to pollutant degradation. Fe-doped TiO2 has also been reported to accelerate photodegradation and enhance optical, electronic, and antibacterial potentials [11]. In addition, silica particles were also used in our studies as conjugating agents for photocatalyst iron doped nanotitania, ensuring a stable attachment to concrete sphere. The reason was to increase the specific surface area of nano photocatayst, which in turn improves photo-catalytic efficiency, enhances thermal resistance, and avoids aggregation of iron-doped nano titania [12].
References cited in the present disclosure are not always previous art, and citing them does not represent a recognition that such references are prior art in any jurisdiction. All publications, patents, and patent applications incorporated by reference herein are incorporated by reference to the same extent as if each individual or patent application were specifically and individually indicated to be incorporated by reference.
A few relevant patents were mentioned in Table 8 related to TiO2 as a photocatalyst with others, however, none of them is related to the kind of our product, i.e., concrete supported photocatalysts where the epoxy resin was used as a strong binding agent to bind photocatalysts (nano titania) stably with green concrete mortar.


OBJECTS OF THE INVENTION: -
The objective of the present invention is to develop a method to synthesize green concrete supported nanophotocatalyst bead comprising of nanophotocatalysts on green concrete bead for the degradation of multiple toxic pollutants under solar irradiation, visible or UV light.
A further objective of the present invention is to provide a powdered nanophotocatalyst system comprising iron doped nanotitania and conjugated with silica oxide, which promotes photodegradation of multiple aqueous pollutants under UV, visible or sun light.
Yet another objective of the present invention is to enhance the shelf life of the photocatalyst coating on green concrete bead surface by using epoxy resin binding as to improve their compressive strength and acidic resistance, and make them reusable.
Yet another objective of the present invention is to achieve antibacterial potential of prepared photocatalyst coated green concrete bead.
SUMMARY OF THE INVENTION: -
This summary introduces simplified concepts of this invention which would be discussed further in detailed description.
Present invention relates to a product 'iron doped nanotitania and conjugated with silica composite (Fe-nanoTiO2/SiO2)', wherein the composite deposited on green concrete beads (GCBs) surface where surface binding was mediated by epoxy resin (ER) and Fe-nanoTiO2/SiO2 composite for remediation of aqueous pollutants.
In some aspects, according to the present disclosure, the photocatalyst was immobilized on green concrete beads (GCBs), deals with the concept of 'Concrete Support Photocatalyst', where GCBs were prepared using coal fly ash (CFA)- derived zeolite, open Portland cement (OPC) and aggregate mixture.
In one aspect, the disclosure also relates to the decontamination of both gram-positive and gram-negative bacteria such as E. coli and S. aureus by the photocatalyst, where Fe-nanoTiO2/SiO2 acts as photocatalyst and green concrete beads (GCBs) act as the solid support system.
In some aspect, the preparation method of photocatalyst bead as disclosed in the present invention is economical and industrially sustainable as the fabrication method requires minimal quantity of chemical reagents, easy to scale-up and provides a simple regeneration process that can be used for photocatalytic degradation of aqueous pollutants under UV radiation, visible light and sunlight.
In one aspect, the present disclosure provides concrete supported photocatalyst (CSP) stability under wide range of photocatalysts in any acidic and alkaline environment.
BRIEF DESCRIPTION OF THE DRAWING
Fig. 1: Schematic diagram of c-GCB50 as shown in fig. 2 (e) where c-GCB50 comprises of core support as GCB50 and photocatalysts (Fe-nanoTiO2/SiO2/ER). Here, ER implies to epoxy resin.
Fig. 2: Digital image of (a) Coal fly ash (CFA) (b) CFA-derived zeolite (c) cylinder GCB shaped structure prepared for physio-mechanical testing (d) GCB50 (e) photocatalyst (Fe-nanoTiO2/SiO2) coated green concrete bead (c-GCB50).
Fig. 3: XRD analyses of (a) zeolite (b) Coal fly ash (CFA) (c) different proportions of Fe-nanoTiO2/SiO2 (b) GCB50 at 0.5 days, 3 days, 7 days, 14 days and 28 days.
Fig. 4: FTIR spectra of (a) Fe-dope nanoTiO2 and (b) Fe-doped nanoTiO2/SiO2
Fig. 5: Energy band gap analysis of (a) nanoTiO2 (b) Fe-nanoTiO2 (c) Fe-nanoTiO2/SiO2
Fig. 6: (a) FESEM image of Fe-nTiO2/SiO2 (b) EDS analysis of Fe-nanoTiO2/SiO2 (c) SEM image of GMB50 (d) (d) EDS analysis of GCB50 (e) SEM image of Fe-nanoTiO2/SiO2/ER (f) EDS analysis of Fe-nanoTiO2/SiO2/ER
Fig. 7: Compressive strength of GCB0 and c-GCB50 after 28 days of water curing.
Fig. 8: Water absorption behaviour of different GMB samples after 24h.
Fig. 9: Durability study of c-GCB50 and GCB50 in 1 molarity of (a) sulphuric acid and (b) hydrochloric acid where GCB50: 50% of zeolite content with open Portland cement (OPC); c-GCB50: photocatalyst coated GCB.
Fig. 10: Antibacterial activity of c-GCB50 or CSP
Fig. 11: Reusability study of c-GCB50 or CSP
Fig. 12: Photocatalytic degradation analysis of 20 ppm (a) CR (b) CV (c) MB (d) 4NP (e) CPS by c-GCB50 or CSP
DETAILED DESCRIPTION OF THE INVENTION
Various exemplary embodiments of the present disclosure are described herein below with reference to the accompanying figures in the specification to enable a person of ordinary skill in the art to make and use the present disclosure.
The terminology used herein is for describing particular/embodiments only and is not intended to limit the invention.
It will be further understood that the terms "comprises," and/or "comprising," and/or "including," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude or rule out the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
The term "conjugate" or "composite" is used throughout the specification before the numeric values shall include ±10% of the indicated value.
While this detailed description has disclosed certain specific embodiments for illustrative purposes, various modifications will be apparent to those skilled in the art which do not constitute departures from the spirit and scope of the invention as defined in the following claims, and it is to be distinctly understood that the preceding descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.
Generally, Fe-nanoTiO2 and SiO2 based composite produced in powder forms and when these are added to water, they become milky solution. Utilizing Fe-nanoTiO2/SiO2 suspension results in more desirable degradation efficiency as a result of improved mass transfer applications and enhanced exposure of the catalyst surface. The primary disadvantage of using suspended catalyst is its separation from the aqueous solution following treatment, which hinders its commercial application and efficiency.
The present invention discloses the development of iron doped nanotitania conjugated with silica particles (Fe-nanoTiO2/SiO2), preferably dip coated on the surface of green concrete beads (GCB50) using epoxy resin (ER), is said to be photocatalyst coated GCB (c-GCB). The c-GCB here is also named as Concrete Supported Photocatalyst or in short 'CSP'. The disclosed c-GCB or CSP was used for effective degradation of industrial toxic pollutants in aqueous solution.
Most of the catalysts available in the market are in powder or solid form. Preparation methods of available solid photocatalysts are costly, time consuming and demands for high initial set-up investment. However, the invention discloses the preparation of a low cost concrete spherical support for photocatalyst named "Concrete Supported Photocatalyst" (CSP) bead. Moreover, the method of preparation is economical and does not only consume industrial waste materials such as coal fly ash (CFA)-derived zeolite but also minimises the dose of photocatalyst. Thus, overall cost of the operational process for preparing CSP is substantially reduced.
In one embodiment, according to present invention, iron doped titania conjugated with silica particles was prepared through a simple wet chemical method where following steps were adopted:
a. Fe doped nanoTiO2 particles (Fe-nanoTiO2) was synthesized using sol-gel method
b. SiO2 conjugated Fe-nanoTiO2 composite was prepared using precipitation method
c. Photocatalyst (Fe-nanoTiO2/SiO2) were homogeneously mixed with epoxy resin (ER) using sonication.
d. Composite (Fe-nanoTiO2/SiO2) were prepared by dip coating of GCB-50 in epoxy resin and photocatalyst solution. Where green concrete beads (GCBs) were prepared using zeolite, Portland cement and aggregate mixture and act as support system.
In one aspect of the above embodiment, GCBs can be spherical or rod-shaped with diameter ranging from 1.0 cm to about 5.0 cm, preferably 2.5 cm to about 4.0 cm, and more preferably about 3.3 ± 0.5 cm, with an aspect ratio of 1.5:1 to 2:1 (for rod-shaped GCBs), for achieving maximum pollutant remediation efficiency as described in our invention. In another aspect, GCB's dimensions can vary depending upon the requirement of the user such as volume of waste treatment tank or the productivity.
In one embodiment, according to the present invention, the CSP (Concrete Supported Photocatalyst) or Fe-nanoTiO2 conjugated with SiO2 particles on the surface of GCBs, can be used for the photodegradation of various industrial toxic pollutants in aqueous solution using UV light, visible light and solar light as the energy source.
In another embodiment, according to the present invention, the composite prepared by iron doping in titania nanoparticles characteristically triggered photocatalytic reaction under visible light or sun light.
In a related aspect of the above embodiment, the photocatalytic reaction efficiency can be further improved by the conjugation of SiO2 particles with Fe-nanoTiO2. The SiO2 particles enhances the overall surface area of the photocatalyst (Fe-nanoTiO2/SiO2) which provides more active sites for photocatalytic reactions, enhancing the efficiency of the photocatalyst coated on GCB50 (c-GCB50 or CSP).
In another related aspect of the above embodiment, the composite are dip coated on GCBs, wherein GCBs may be used as the support system for the photocatalyst (Fe-nanoTiO2/SiO2). Such conjugation of photocatalyst with GCB provides them a better support system and exposure to the pollutants that can lead to enhanced degradation rate by increasing the surface contact time. The primary benefits of the claimed nanocomposite are attributable to the composition and its preparation, making it a highly effective, eco-friendly photocatalyst bead which is easy to fabricate and requires a minimal amount of chemical reagents, easy to use and simple regeneration process that can be used for photocatalytic degradation using UV light, visible light or sun light as energy source.
In one embodiment, the present invention provides photocatalyst coated green concrete beads (Fe-nanoTiO2/SiO2@GCB) or CSP wherein iron doped nanotitania conjugated with silica particles and their dip-coating on GCBs (prepared using a mixed slurry of zeolite, cement and aggregate mix.) using epoxy resin (ER) can be readily used for photo-degradation of various pollutants such as dyes like Congo red (CR), Crystal Violet (CV), Methyl Blue (MB), a phenolic pollutant 4-nitrophenol (4NP) and a pesticide, chlorpyrifos (CPS).
Further, when compared to prior art disclosure, the presently disclosed Fe-nanoTiO2/SiO2 composite provided better photo-catalytic activity in exemplary embodiments successfully degraded 20 ppm of Congo red (CR), Crystal Violet (CV), Methyl Blue (MB), 4-nitrophenol (4NP) and Chlorpyrifos (CPS).in 2.5 h under sun light. In some aspects the photocatalyst (Fe-nanoTiO2/SiO2) according to the present disclosure was proved to be highly efficient in degrading aqueous pollutants containing about 10 ppm to 500 ppm of different pollutants in a span of 1.5 h to 15 h.
In some embodiment, according to present disclosure the catalyst as prepared is easy and simple to handle, can degrade multiple pollutants in aqueous medium and very much suitable for utilization and extension. Hence, it enhances the reusability of the same catalyst for multiple cycles or remediation process. In one aspect it is working with nearly or more than to 81% efficiency up to 15 cycles.
After all, the present disclosure provides a simple and easy to handle photocatalyst which requires limited number of chemicals for its preparation and is an effective and eco-friendly photocatalyst which can be applied for photocatalytic degradation of multiple aquatic pollutants where the sunlight acts as sole energy source.
In one embodiment, the present invention provides a method for the preparation of photocatalyst (Fe-nanoTiO2/SiO2) wherein the said method comprises the following steps:
a. Adding salt and urea into milli-Q water;
b. Adding titanium isopropoxide (TTIP) drop-wise in the solution prepared in step 'a';
c. Continuous stirring of the solution prepared in step 'b' in a range of 400-600 rpm, and at a temperature of 70-90º C for 1-3 h;
d. The precipitate was collected, washed, and dried overnight at 60-90˚ C in step 'c'. Thus, Fe-nanoTiO2 was obtained;
e. Addition of prepared Fe-nanoTiO2 (mentioned in step 'd') to tetraethyl orthosilicate (TEOS) with 1M HCl solution. This solution was hydrolysed for 24 hours while maintaining a pH of 5.0 using a 1M alkaline solution, wherein alkaline solution could be sodium hydroxide or potassium hydroxide or ammonium hydroxide solution.
f. The precipitate was collected, washed, and dried overnight at 80-100˚ C in step 'e'. Hence, Fe-nanoTiO2/SiO2 was prepared.
In yet another embodiment, the method for the preparation of coated photocatalyst on the surface of green concrete beads (Fe-nanoTiO2/SiO2@GCB50) using epoxy resin (ER), also called CSP, comprises of a spherical or rod-shaped core made of green concrete bead (GCB50) and the core is coated by a layer of iron-doped titania nanoparticles conjugated with silica particles (Fe-nanoTiO2/SiO2), said to be photocatalyst, the and method comprises the following steps:
a. Coal fly ash (CFA) was heated at 800-1000º C for 1 h.
b. Add 1N HCl to heated CFA prepared in step 'a';
c. Wash acid-treated CFA as mentioned in step 'b' multiple times with deionized water.
d. Sodium hydroxide was fused with modified CFA as prepared in step 'c' in a ratio of 1.0-1.5 and heated at 500-600º C for 1-2 h;
e. Wash modified CFA prepared in step 'd' multiple times. Thus, CFA-derived zeolite was prepared.
f. CFA-derived zeolite prepared in step 'e', cement and sand aggregates were uniformly mixed in a ratio of 1:1:2 (W/W) %;
g. The obtained slurry prepared in step 'f' was moulded into beads of varying shapes such as rod and spherical with a diameter of up to 50 mm and height (for rod shape) up to 100 mm, and molded after 6 h. Thus, GCB50 was prepared.
h. GCB50, prepared in step 'g', was water-cured for 28 days.
i. Adding titanium isopropoxide (TTIP), ferric chloride and urea in the solution prepared in milli-Q water;
j. Continuous stirring in a range of 400-600 rpm, and at a temperature of 70-90º C for 1-3 h of the solution prepared in step 'i';
k. The precipitate was collected, washed, and dried overnight at 60-90˚ C in step 'j'. Thus, Fe-naoTiO2 was obtained;
l. Addition of prepared Fe-nanoTiO2 mentioned in step 'k' to tetraethyl orthosilicate (TEOS) with 1M HCl solution. This solution was hydrolysed for 24 hours while maintaining a pH of 5.0 using a 1M alkaline solution, wherein alkaline solution could be sodium hydroxide or potassium hydroxide or ammonium hydroxide solution.
m. The precipitate was collected, washed, and dried overnight at 80-100˚ C in step 'l'. Thus, Fe-nanoTiO2/SiO2 was prepared.
n. Adding Fe-nanoTiO2/SiO2 in epoxy resin (ER) was uniformly dispersed;
o. GCB50 or CSP, as mentioned in step 'h', was dip-coated in the solution prepared in step 'n' and dried for two days at room temperature. Thus, c-GCB50 (coated GCB50) was prepared.
In one aspect, according to the above embodiment the ferrous or ferric salts used in step 'i' is selected from ferric chloride, ferric sulphate, ferric nitrate, ferrous sulphate or combination thereof. In one preferred aspect the salt is ferric chloride.
In yet another aspect, according to the above embodiment the water used in step 'i' is purified water such as milli-Q water.
In another aspect, according to the above embodiment, the stirring in step 'j' is done at rpm of 300-900 rpm, more preferably 450-500 rpm.
In a further aspect, according to the above embodiment, during the stirring step 'j' the temperature of the solution is maintained at a temperature of about 70-100 ºC, preferably at about 80-90 ºC, for about 2-6 h, more preferably for about 3.5-4.0 h.
In yet another aspect, according to the above embodiment, in step 'f' zeolite, Portland cement and sand aggregates were mixed differently with the same ratio of 1:1:1,1:1:3, 1:1:4, 1:1:5 and 1:1:6 ratios.
In yet another aspect, according to the above embodiment, the dimensions (diameter) of the green mortar beads (both spherical or rod-shaped) vary ranging from 1.0 cm to about 5.0 cm, preferably 2.5 cm to about 4.0 cm, more preferably about 3.3 ± 0.5 cm, with an aspect ratio of 1.5:1.
In a related aspect, according to the above embodiment, the pH of solution in step 'l' is about pH 3.5 - 7.5, preferably pH 5±0.25.
In one yet another aspect, of the above embodiment, in the step 'h', GCBs are water-cured for about 1-28 days, preferably for about 3 - 21 days, more preferably for about 7 days and dried.
In another aspect, of the above embodiment, in step 'o' c-GCBs' were cured at 20-60ºC, preferably 25-45ºC, more preferably for about 35ºC. In a related aspect curing time was continued for 2-48 h, preferably for about 6-36 h, more preferably for 18±2 h.
In some embodiments according to the present invention for the preparation of the GCB50, different types of cement such as open Portland cement, and slag cement can be used to produce GCB50, as mentioned in step 'h'. In one preferred aspect the cement used is open Portland cement.

EXAMPLES:
Detailed embodiments of the present invention are disclosed herein with the help of examples with reference to the accompanying drawing; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms.
Example 1: Preparation of iron doped titanium oxide nanoparticles (Fe-nanoTiO2)
300 mg of urea and 2.5 mg of ferric chloride are homogeneously mixed with 50 ml of milli-Q water. 5 ml of Titanium isopropoxide (TTIP) as precursor was added drop-wise. The resulting suspension was stirred magnetically for 3 h at 75ºC. After that, the mixture was centrifuged and washed repeatedly 3-6 times with milli-Q water, the collected residue was dried over-night at 60ºC. The yield of the synthesized Fe-nanoTiO2 was found to be about 50%.
Example 2: Preparation of iron doped titanium oxide nanoparticles (Fe-nanoTiO2/SiO2)
In a beaker, distilled water, 0.5% of ferric chloride and 0.3 g urea were mixed and stirred for 5 min. Titanium tetra isopropoxide (TTIP) was added drop-by-drop into the mixture, and the resulting suspension was agitated for 30 min. Then, this mixture was placed in a water bath for one hour at 90 °C. The separated product from centrifuging of the required mixture was collected and dried for 12 h at 80 °C. Then TEOS precursor was added to Fe-nanoTiO2/SiO2 solution in a ratio of 1:3 and hydrolysed with 1N HCl solution, followed by stirring for 24 h for obtaining white solution. The solution was further dried over-night at 80˚C. Then this powder was annealed at 550˚C for 2 h.
EXAMPLE 3: Preparation of green mortar beads (GCBs)
Green concrete beads (as in Fig.1) or in short 'GCB', were prepared by using a mould for dimension 3.3 ± 0.5 cm. CFA-derived zeolite, Portland cement, water and sand aggregates were mixed with in 1:1:2 (W/W) % and (water/solid mix.) ratio was 0.6 (V/W%). The resulting paste was moulded for 6 h, demoulded and dried at room temperature for 72 h. Then GMBs composites were prepared with 10%, 20%, 30%, 40% and 50% zeolite as to replace that amount of cement partially. As we observe from table 1, there was reduction in compressive strength after addition of more than 30% of CFA-derived zeolite. At GCB50, there was 32.54 % less compressive strength as compared to GCB0 due to improper pozzolanic and hydration reactions inside them. So, it is advisable to add more than 50 % CFA-derived zeolite with cement in concrete.
For compressive testing, GCBs were prepared into cylindrical form in different mass ratio of zeolite and cement which are further denoted as GCB0, GCB10, GCB20, GCB30, GCB40, GCB50 and c-GCB50 where c-GCB50 implies to Fe-nanoTiO2/SiO2 on GCB50 using ER, also called Concrete supported photocatalyst (CSP). And for other studies, GCBs were prepared into spherical form, shown Fig.1. Further they were subjected to water-curing for 28 days. Thus, photocatalyst beads are ready for further characterization and applications.


Table 1: Compressive strength and water absorption of GCBs at different amount % of cement and CFA-derived zeolite
Sample
Green concrete beads (GCBs) Zeolite
%(W/W) Portland Cement
%(W/W) Epoxy Resin (ER)
%(V/W) Nanophoto catalysts
%(W/W) Water absorption
(%) Compressive strength (MPa)
GCB0 0 100 0 0 6.95 10.673
GCB10 10 90 0 0 7.96 14.83
GCB20 20 80 0 0 8.67 13.64
GCB30 30 70 0 0 9.65 12.82
GCB40 40 60 0 0 10.6 8.22
GCB50 50 50 0 0 11.54 7.2
c-GCB50 50 50 10 0.3 4.7 23.48
c-GCB means photocatalyst coated on GCB using ER
EXAMPLE 4: Preparation of photocatalysts with varying content
Table 2: Varying amount of photocatalysts loaded on GCB50 towards pollutants remediation
Green concrete bead (GCB) FeCl3
(W in mg) TTIP
(V in ml) TEOS
(V in ml) Band gap energy (eV) Degradation rate constant
(10-3 min-1)
CFA derived zeolite like materials
(in gm) Portland Cement
(in gm) Water to binder ratio
9 9 0.5 0 5 0 3.3 9.23
9 9 0.5 12.5 5 0 3.02 11.35
9 9 0.5 25 5 0 2.88 13.02
9 9 0.5 25 5 8.33 2.96 15.1
9 9 0.5 25 5 5 2.94 15.7
9 9 0.5 25 5 3.57 2.89 16.02
Where FeCl3 implies to Ferric chloride and TTIP implies to Titanium isopropoxide
The required varying content of photocatalysts coated on GCB50 using ER have been analysed under sunlight at (TTIP/ TEOS = 0.6). Here, nanoTiO2 is obtained from Titanium isopropoxide whose yielding efficiency is 40 % and SiO2 is obtained from Tetraethyl orthosilicate whose yielding efficiency is 80 %. Bandgap energy (Eg) has been calculated using Tauc plot. Here, degradation rate constant was given for Congo red in table 2. Kinetics of photocatalytic degradation of aqueous pollutants (like Congo red (CR), Crystal Violet (CV), Methyl Blue (MB 4-nitrophenol (4NP) and chlorpyrifos (CPS)) was done using pseudo first order (PFO). Chemical oxygen demand (COD) analysis was done to confirm about pollutants remediation at the end of 2.5 h as shown in table 5.
Example 5: Preparation of epoxy resin (ER) coated GCBs.
Table 3: Varying composition of epoxy resin (Vol/W) % with respect to GCB
Samples
Coated Green concrete beads (c-GCBs) Compressive strength (MPa)
Quantity of epoxy resin (ER) (Vol/W) %
2.5 5 10 15
c-GCB0 16.31 19.50 23.52 24.88
c-GCB10 22.48 27.71 29.48 30.27
c-GCB20 20.83 22.48 27.66 28.29
c-GCB30 18.5 21.3 24.43 26.15
c-GCB40 17.34 20.72 23.56 24.93
c-GCB50 16.48 20.07 23.48 24.16

The required percentage amount of epoxy resin (ER) (10%) and Fe-nanoTiO2/SiO2 (0.3%) with respect to the weight of GCB was added, as shown in Fig.1, was stirred for next 30 min. It should be noted that the ratio of hardener to ER ratio was 0.5 (w/w%). Using 3 times dip coating technique, GCB samples were dipped into the solution for next 15 min, and dried before re-dipping. Further, GCBs were allowed for curing till next 2 days at room temperature and is said to be coated GCBs (c-GCBs). Thus, coated c-GCB10, c-GCB20, c-GCB30, c-GCB40, c-GCB50 were prepared. From table 3, we observed that optimum resin content for maximum compressive strength is nearly 10 %, beyond it there is approximately same compressive strength at 15 %. From 2.5 % and 5 %, there was sufficient enhancement in compressive strength. At 10 % ER, there was proper interaction of reactive epoxide group with C-S-H products on surface of GCBs during their curing periods, and resulted into strong bonded interface. Hence we selected c-GMB50 at 10 % of ER composition (V/W) %. It is also said Concrete Supported Photocatalyst (CSP).
Example 6: Characterization of the coated green concrete beads
Fig. 3 describes the X-ray diffraction patterns of photocatalyst (Fe-nanoTiO2/SiO2) samples. These results show that samples with lower silicon content (rich in nanoTiO2) have highly intense reflections at 2θ at 25º (characteristics peak of anatase titanium oxide). Furthermore, the silica content rises, the specific surface area increases, resulting in low strong reflections in the same spots, indicating the presence of long-range disorder. For zeolite, intense peaks obtained were 14.12º, 26.83º, 31.9º, 35.03º, 38.02º, 43.22º, 52.49º and 58.74º; all were in proper agreement of P (Na-zeolite). Here, P stands for Na6Al6Si10O12.12H2O. At peak 24.55º, there was still small amount of quartz. XRD pattern of GCB50 revealed the presence of cement hydration crystalline compounds (quartz, calcium carbonate, calcium silicate and ettringite) from 0.5 days to 28 days by presence of sharp and intense peaks. Peaks observed at 2θ on 21º, 41º, 61º & 70º were indexed to quartz structure. Peaks at 2θ on 25º & 38º were attributed to calcium silicates; and 28º & 51º and 33º were indexed to ettringite respectively.
Fig. 4 shows the FTIR spectra of Fe-nanoTiO2 /SiO2 with ER in the range order of 500 cm−1 to 4000 cm−1 has been studied. The broad peak at 1064 cm-1 due to the production of oxirane-Si-O-Ti bonds, and metal oxygen bonding peaks such as 765 cm-1 and 870 cm-1. Oxirane group has gained from epoxy resin. The observed peak at 870 cm-1 validates the symmetric stretching in the Si-O-Si bond. The wavelength of Ti-O bridge stretched bonds is 765 cm-1. At 3450 cm-1 and 1635 cm-1, OH bending vibrations are attributed to chemisorbed water molecules. At 460 cm-1 to 480 cm-1, a Ti-O stretching bond was detected. At 700 - 800 cm-1, there is presence of iron oxide bond.
Fig. 5 shows the optical band gap energy (Eg) of prepared products where Fe-nanoTiO2 (Eg = 2.886) and Fe-nanoTiO2/SiO2 (2.968 eV) and showed lower band gap energy than the bulk nTiO2 (3.4 eV). The Eg of Fe-nanoTiO2 decreased significantly, which paved the way for a variety of applications, including photocatalysis and photovoltaic technologies that could function in the visible range. Furthermore, the position of the absorption edge was shown to be sensitive based on the type of bond formation between metal oxides, i.e., the coordination number influences not only the Eg but also their size and electrical behaviour.
Fig. 6 shows field emission scanning electron microscopy (FESEM) images of Fe-nanoTiO2 with average particle size of 136 nm. Fe-nanoTiO2 crystallizes and its combination with bigger SiO2 i.e., nano-photocatalyst (Fe-nanoTiO2/SiO2) with average particle size approximately 1532.6 nm. As shown in fig.5. (e) & fig.5. (f). Fe-nanoTiO2/SiO2 had better dispersion of nano-photocatalysts with epoxy resin, confirmed by its EDS analysis with the presence of Ti, Si, N & O. SEM image analysis of GCBs has dense or anhydrous zeolite or cement products. Its EDS analysis shows that presence of Ca, Si, Al and O indicate abundance of C-S-H gel, C-A-H, Ca(OH)2, dicalcium aluminate & tricalcium aluminate as their major products.
EXAMPLE 7: Compressive strength and water absorption analysis of coated green concrete bead (c-GCB50) or CSP
Fig. 7 depicts the compressive strengths of the cylindrical GCBs in Table 1. It can be observed from Table 1 that, 10% of partial replacement of zeolite for preparing GCB10 has 38.89% higher compressive strength than to GCB0. Under the same 20% zeolite replacement for GCB30, there is still more 27.79% more compressive strength. But the replacement of zeolite was 30-50 %, the strengths was found to be compromised. However, nano-photocatalysts (Fe-nTiO2/SiO2), were further loaded on zeolite mortar using epoxy resin as desired earlier. As epoxy resin has high adhesive ability, it forms strong bonds with cementitious matrix. Those strong bonds help to sustain even more loads of 23.48 MPa.
Fig.8 shows that the percentage water absorption of GCB0 has 6.958% and GCB50 has 11.545% in Table 1. c-GCB50 showed lowest water absorption activity i.e., 4.7%. The reason could be the filling up pores of GCB50 by epoxy resin with photocatalysts. This found the lower porosity while enhances the compressive strength and density.
EXAMPLE 8: Durability Study of c-GCB50 or CSP
Fig. 9 shows durability Studies of GCB50 and c-GCB50 at room temperature. as shown in Fig.1(b) and (c) were submerged in 1M H2SO4 and HCl acid solution for effective coating resistance; initially absorption rose with increasing duration at high rate, saturated and began to lower down for GCB50 for four-days study. Although GCB50 was saturated in 24 h. For c-GCB50 or CSP, absorption rate increased non-linearly or time-independently. GCB50 was started to corrode after few hours of exposing to acidic environment but c-GCB50 had high water absorption ability and corrosive resistance even after 96 h analysis.
EXAMPLE 9: Antibacterial Study of c-GMB50 or CSP
Fig. 10 shows antibacterial analysis of bacteria such as E. coli as an important study which may cause serious threats to some structures exposed to harsh environmental conditions. As amount of photocatalysts with GCB50 have been varied and analysed using well diffusion and broth dilution method. Here sample S1, S2, S3 and S4 represents 0.1 mg/ml, 0.2 mg/ml, 0.25 mg/ml and 0.3 mg/ml respectively. Fig.10. (a) shows results of broth dilution method and fig.10 (b) for well diffusion method. Thus c-GCB50 (having 0.3 mg/ml) had 19.6 % survival bacterial rate after 24 h of incubation. The prime reason behind it that c-GCB50 might exhibit restricted bacterial growth; when there would be direct contact of pathogens with c-GCB50.
EXAMPLE 10: Photocatalytic Study of c-GMB50 or CSP
Fig. 12 shows photodegradation studies by c-GCB50 for aqueous pollutants for 20 ppm of 100 ml at pH 7 was stirred and subjected to sun radiation for anionic dye (Congo red) & cationic dyes (crystal violet and methylene dye). 4-nitrophenol (4NP) and chlorpyrifos (CPS) are taken as model nitrobenzene and pesticides. Degradation studies are further described in the plot of C/C0 versus lighted time given in fig.9. Here, C0 is the initial pollutant concentration, while C is the pollutant concentration at time 't'. Variations in pH can alter duration of pollutant's remediation but possesses no significant effect on c-GCB50 as shown in fig. 9.
During 1st cycle, their degradation efficiencies are 99.6, 98.2, 97.87, 94.49 % and 92.42 % as shown in table 5. Their calculated values for apparent rate constants (kapp) and determining reliability coefficients for best fitting curves has been reported in table 4.
Table 4: Kinetic study for the mentioned pollutants degradation
Dye sample Kapp (h-1) R2
CR 0.01078 0.994
CV 0.00892 0.972
MB 0.0152 0.919
4NP 0.0181 0.931
CPS 0.0143 0.946



EXAMPLE 11: Chemical oxygen demand (COD) Analysis of Aqueous pollutants
COD was determined by using titration method at the end of 150 min, as reported in table 5. It shows the presence of biodegradability of the required samples and also monitors their removal or presence of organic matters during degradation of the above pollutants. Here, all the above-mentioned aqueous pollutants were degraded under solar irradiation. Then their COD analysis was performed.
Table 5: Degradation and COD analysis for the mentioned pollutants
Dye sample Degradation (%) COD reduction (%)
CR 99.6 95.38
CV 98.2 92.64
MB 97.87 90.17
4NP 94.49 88.49
CPS 92.42 83.61





EXAMPLE 12: Reusability Study of c-GMB50 or CSP
Fig. 11 shows reusability analysis for accessing the application of photocatalytic ability of used c-GCB50 in table 6. where c-GCB50 were subjected to fifteen adsorption- desorption cycles. It has shown that the efficient and effective regeneration capacity of c-GCB50 even after 15 cycles. A slight drop in degradation efficiency after 5th cycle is 95.89 % (Congo red), 93.78 % (crystal violet), 91.26 % (methylene blue), 89.84 % (4-nitrophenol), 87.25 % (Chlorpyrifos) respectively and after 15th cycles reusability study of c-GCB50 was for Congo red (91.36 %), crystal violet (89.21 %), methylene blue (86.67 %), (814.31 %) 4NP and (81.74 %) Chlorpyrifos. This may be due to catalyst deactivation, surface contamination, structural changes or photo-corrosion of the solid catalysts. As repeated usage of this invention has its reduced degradation efficacy because available active sites on the surface of photocatalyst were getting deactivated by reaction by-products or impurities or adsorbed species from dye pollutants for hindering catalytic activity.
Table 6: Degradation efficiency of c-GCB50 for the mentioned aqueous pollutants
Azo dyes Efficiency (%) after 5th cycle Efficiency (%) after 15th cycle
CR 94.08 91.36
CV 92.5 89.21
MB 91.26 86.67
4NP 88.94 84.11
CPS 87.25 81.74

EXAMPLE 13: Comparison Study
A comparison table is presented in table 7 to aid comprehension of the present innovation and its benefits. Although there are a few publications on photocatalyst coating on concrete, there is no information on photocatalyst coating on GCBs using epoxy resin (Fe-nanoTiO2/SiO2) comprising iron-doped nanotitania particles conjugated with silica particles for enhanced durability and photocatalytic effect.
Table 7: A comparison table on photocatalytic degradation of pollutants
Catalysts Nature of photocatalyst Pollutants Concentration (ppm) Light Source Degradation % Time (min) Reference
TiO2/SiO2@Cement mortar Photocatalyst coated on cement mortar block RhB 0.1 UV light 90 < 240-360 [13]
TiO2/SiO2@Cement concrete Photocatalysts coated on cement concrete block MB 10 Visible light 95 360 [14]
N-TiO2/SiO2@concrete Photocatalysts on concrete surface MB 2 UV light 95 300 [15]
ZnO- TiO2/TH Photocatalysts coated on Thermite Hill MB 50 Sun light 99.5 480 [16]
Fe-TiO2
Ce-TiO2
Co-TiO2
Cu-TiO2 Powdered photocatalyst MO 10 UV light 79
91.5
100
90 300 [17]
W-nTiO2 Powdered Photocatalyst MB
Basic Violet 10 UV light 98.3
72.58 180 [18]
SiO2/nTiO2@cement Photocatalyst coated on white cement slab MB 20 UV light 95.7 300 [19]
microTiO2/white cement Photocatalyst coated on white cement slab RhB 100 UV light 75 480 [20]
Titanium coated cement Photocatalyst coated on cement block Tartrazine 20 Sunlight 93 210 [22]
TiO2 based cement Photocatalyst blended with cement RhB 30 Sunlight ~99 7200 [23]
*Fe-nanoTiO2/SiO2
@GCB50 Photocatalyst coated on green concrete spherical bead using epoxy resin MB
CR
CV
4NP
CPS 20 Sunlight 97.87
99.6
98.2
94.49
92.42 150 This work
* Implies for iron doping with nano-titanium dioxide conjugated with silica coated on GCB50.
EXAMPLE 14: Advantages
In one aspect of the prepared coated green concrete bead (c-GCB50) comprised wherein beads are produced using modification of industrial waste and photocatalysts are produced using minimal quantity of chemicals, c-GCB50 possesses outstanding photodegradation performance for diverse aquatic pollutants such as CR, MO, 4NP and CPS. It has a broader application against other multiple pollutants. It is reusable, scalable and economically inexpensive. Furthermore, the entire process is environmentally friendly and energy efficient. This makes the described catalyst not only technically superior, but also an economically significant undertaking for pollutants remediation.
The benefits and advantages are that the present invention may bring were discussed above in terms of certain embodiments. These advantages and benefits, as well as any aspects or limits that may cause them to arise or become more evident, are not to be interpreted as critical, required, or important features of any or all embodiments.
While the present invention has been discussed with specific embodiments, it should be noted that the embodiments are merely illustrative and that the invention is not limited to these embodiments. There are numerous variants, modifications, additions, and enhancements that can be made to the embodiments described above. These variants, alterations, additions, and enhancements are thought to be within the scope of the invention.

ABBREVIATIONS
GCB - Green concrete bead
TTIP - Titanium tetra isopropoxide
TiO2 - Titania or titanium oxide
Fe-nanoTiO2 - Iron doped Titanium dioxide
SiO2 - Silica or silicon oxide
Fe-nanoTiO2/SiO2 - Photocatalyst
ER - Epoxy resin
c-GCB - Coated green concrete beads
Fe-nanoTiO2/SiO2@GCB50 - Fe-nanoTiO2/SiO2 coated GCB50 using ER
MB - Methylene blue
CV - Crystal violet
CR - Crystal red
4NP - 4-nitrophenol
CPS - Chlorpyrifos
XRD - X-ray diffraction
SEM - Scanning electron microscopy
FESEM - Field emission SEM
FTIR - Fourier transform infrared spectroscopy
UV- Ultra violet
COD - Chemical oxygen demand
, Claims:1. A coated Concrete supported photocatalyst (CSP) comprising:
a) a spherical or rod-shaped core made of green concrete bead (GCB50);
b) the core is coated by a layer of iron-doped nanotitania particles conjugated with silica particles (Fe-nanoTiO2/SiO2), said to be photocatalyst;
c) the layer is bonded to the GCB50 surface using an epoxy resin.
2. The CSP, as claimed in claim 1, wherein the photocatalysis induces the pollutants removal, including azo dyes (Congo red, crystal violet, methylene blue), 4-nitrophenol and chlorpyriphos in the presence of sunlight, visible or UV light.
3. The CSP, as claimed in claim 1, wherein the photocatalyst (Fe-nanoTiO2/SiO2), has an antibacterial effect against a wide range of bacteria such as E. coli and S. aureus.
4. A method for the preparation of the CSP, as claimed in claim 1, comprises the following steps:
a. Coal fly ash (CFA) was heated at 800-1000º C for 1 h.
b. Add 1N HCl to heated CFA prepared in step 'a';
c. Wash acid-treated CFA as mentioned in step 'b' multiple times with deionized water.
d. Sodium hydroxide was fused with modified CFA as prepared in step 'c' in a ratio of 1.0-1.5 and heated at 500-600º C for 1-2 h;
e. Wash modified CFA prepared in step 'd' multiple times. Then, CFA-derived zeolite was prepared.
f. FA-derived zeolite prepared in step 'e', cement and sand aggregates were uniformly mixed in a ratio of 1:1:2;
g. The obtained slurry prepared in step 'f' was molded into beads of varying shapes such as rod and spherical with a diameter of up to 50 mm and height (for rod shape) up to 100 mm along with an aspect ratio of 1.5:1 to 2:1 (for rod-shaped GCBs), and molded after 6 h. Thus, GCB50 was prepared.
h. GCB50, prepared in step 'g', was water-cured for 28 days.
i. Different types of cement such as Portland pozzolanic cement, open Portland cement, and slag cement can be used to produce GCB50, as mentioned in step 'f'.
j. Different concentrations of sand with the same ratio of CFA-derived zeolite and cement can be mixed with 1:1:1, 1:1:3, 1:1:4, 1:1:5 and 1:1:6 ratios.
k. Adding salt, wherein salt could be ferric chloride or ferric sulphate or ferrous sulphate or ferric nitrate; and then adding urea into milli-Q water;
l. Adding titanium isopropoxide (TTIP) in the solution prepared in step 'k';
m. Continuous stirring in a range of 400-600 rpm, and at a temperature of 70-90º C for 1-3 h of the solution prepared in step 'l';
n. The precipitate was collected, washed, and dried overnight at 60-90˚ C in step 'm'. Thus, Fe-nanoTiO2 was obtained;
o. Addition of prepared Fe-nanoTiO2 mentioned in step 'n' to tetraethyl orthosilicate (TEOS) with 1M HCl solution. This solution was hydrolysed for 24 h while maintaining a pH of 5.0 using a 1M alkaline solution, wherein alkaline solution could be sodium hydroxide or potassium hydroxide or ammonium hydroxide solution.
p. The precipitate was collected, washed, and dried overnight at 80-100˚ C in step 'o'. Hence, Fe-nanoTiO2/SiO2 was prepared.
q. Fe-nanoTiO2/SiO2 was uniformly dispersed in epoxy resin (ER);
r. GCB50 was dip-coated in the solution, as mentioned in step 'q', and dried for two days at room temperature. Hence, c-GCB50 (coated GCB50) was prepared.

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