معلومات البحث الكاملة في مستودع بيانات الجامعة

عنوان البحث(Papers / Research Title)


Synthesis, characterization, and photocatalytic activity of sonochemical/hydration–dehydration prepared ZnO rod-like architecture nano/ microstructures assisted by a biotemplate


الناشر \ المحرر \ الكاتب (Author / Editor / Publisher)

 
ايناس محمد سلمان الربيعي

Citation Information


ايناس,محمد,سلمان,الربيعي ,Synthesis, characterization, and photocatalytic activity of sonochemical/hydration–dehydration prepared ZnO rod-like architecture nano/ microstructures assisted by a biotemplate , Time 19/01/2017 07:46:05 : كلية العلوم للبنات

وصف الابستركت (Abstract)


ZnO nanoparticles of rod-like architecture have excellent potential to be used in wastewater treatment as a photocatalyst.

الوصف الكامل (Full Abstract)

synthesis, characterization, and photocatalytic activity of sonochemical/ hydration–dehydration prepared zno rod-like architecture nano/microstructures assisted by a biotemplate

ayad f. alkaim a,b, enas m. alrobayic, abrar m. algubilid and aseel m. aljeboreea

adepartment of chemistry, college of science for women, babylon university, hilla, iraq binstitut für technische chemie, leibniz universit?t hannover, hannover, germany cdepartment of laser physics, college of science for women, babylon university, hilla, iraq ddepartment of pharmacy, college of pharmacy, kufa university, najaf, iraq



abstract
zno nanoparticles of rod-like architecture have excellent potential to be used in wastewater treatment as a photocatalyst. they were synthesized by utilizing sonochemical/hydration-
dehydration techniques using glutamine as a biotemplate. the effects of calcination temperatures, that is, 300°c, 500°c, and 700°c, on the crystallinity, optical properties, and photocatalytic activity of synthesized zinc oxide nanoparticles were investigated. x-ray
diffraction (xrd) results indicated that all calcinated samples have a crystalline hexagonal wurtzite structure. morphology and elemental compositions were investigated using field
emission-scanning electron microscopy with energy-dispersive x-ray spectroscopy. the xrd and fourier transform infrared (ftir) spectra revealed that the samples were amorphous at 100°c however, it changed into a crystalline structure amid the calcination process. optical
properties were determined using a uv-visible reflection spectrophotometer and showed abatement in the band gap with increasing annealing temperature. the progress of the
photocatalytic degradation was monitored by a uv-visible spectrophotometer, while the mineralization ability was estimated by total organic carbon tests of zno-calcinated samples. the effect of various operational parameters the photocatalytic efficiency and rate of dye
degradation was studied. high photocatalytic degradation of maxilon blue dye (grl) was found at ph 6.3.

article history
received 21 june 2016
accepted 4 october 2016

keywords
hierarchical zno nanoparticles maxilon blue
dye photocatalytic mineralization






1. introduction

wastewaters from the textile, paper, and some different industries contain lingering colors, which are generally nonbiodegradable [1]. as a result of their complex mol- ecular structures, poor biodegradability, and high solubi- lity, it is very hard to remove dyes from aqueous solutions. consequently, the primary source of aquatic environmental pollution, considerable a color waste- water represents in ecology systems. there are different processes that are applied for the treatment of dye waste effluents (physical or chemical) such as adsorption pro- cesses [2,3]. however, the pollutants cannot be con- verted directly into harmless substances in the wastewater by the adsorption process, because these dye effluents are stable to light and oxidizing agents [4]. thus, the expulsion of these poisonous contaminants from wastewater has attracted immense interest, and many endeavors have been coordinated toward the

improvement of productive and financially savvy treat- ment strategies [5].
in the last few decades, advanced oxidation processes
have been successfully used for the degradation and mineralization of harmful pollutants [6,7]. photocatalysis, a protuberant off-shoot of advanced oxidation pro- cesses, has emerged as one of the most efficient methods for the complete mineralization of toxic organic pollutants [8,9]. the use of low-cost resources such as semiconductor materials, water, and light photons for the generation of reactive oxygen species (ros) further authenticates its efficacy and economic viability [10]. to date, photocatalytic nanomaterials, including metal oxides, have been used for the photoca- talytic degradation of contaminants [11–15]. however, most reported photocatalysts have some disadvantages, which make them unsuitable for any practical appli- cations in wastewater, due to their high cost, low photo- catalytic efficiency, and difficulty to be recycled.



contact ayad f. alkaim alkaimayad@gmail.com ayad_alkaim@yahoo.com alkaim@iftc.uni-hannover.de institut für technische chemie, leibniz universit?t hannover, callinstrasse 3, d-30167 hannover, germany
© 2016 informa uk limited, trading as taylor & francis group





scheme 1. schematic representation of the research work.


comparatively, tio2 and zno nanomaterials show the most promising applications in the environmental treatment field due to their low cost, high photocatalytic efficiency, and environmental sustainability [16–19].
in comparison with tio2, zno shows two important advantages: less charge recombination and higher light absorption below 400 nm [20]. due to its high photocata- lytic activity, zno is also one of the most extensively used photocatalysts, and is used in both acidic and basic media [21,22]. some organic template additives were found to enhance the properties of zno [23]. this is mostly because of their impact by enhancing the physical, chemi- cal, optical, and electrical properties. a portion of the broadly utilized organic templates are polyalkene glycol, triethyl amine, egg white, and ethylene glycol [24,25].
however, there are very few reports on the utilization of biotemplates for the synthesis of zno nanostructures [26]. here, we endeavor to find a more easy method for the synthesis, characterization, and determination of the photocatalytic efficiency of zno nanopowder obtained by using glutamine as a friendly and nontoxic biotem- plate, and water as a green solvent-assisted sonochem- ical/hydration–dehydration process. to the best of our knowledge, the use of glutamine as a biotemplate for the synthesis of zno has not been reported. in this paper, we developed a new and simple synthesis with high photocatalytic properties via sonochemical/ hydration–dehydration assisted by a biotemplate-free aqueous solution method. we also demonstrate the effects of different annealing temperatures of the

prepared zno nanoparticles on their morphology, struc- tural characteristics, and photocatalytic activity.
the photocatalytic efficiency of the synthesized zno
was evaluated by photocatalytic removal/mineralization of aqueous maxilon blue dye. a schematic represen- tation of the research work is presented in scheme 1.



2. experimental details

chemical synthesis of zno nanorods

zno nanoparticles are usually synthesized by the sonochemical/hydration–dehydration method using zn (no3)2•6h2o, h2c2o4, and glutamine (purchased from sigma-aldrich company). all chemicals were used in the synthesis process without any further purification.
an appropriate amount of zinc nitrate zn(no3)2•6h2o (2 mol was first dissolved in 100 ml of deionized water the solution was rapidly stirred using a magnetic stirrer,), 5.0 g of h2c2o4•5h2o, and 4.0 g of glutamine were separately dissolved in 50 ml deionized water. zinc nitrate and oxalic acid components were mixed in a reaction container using an ultrasonic bath with at a frequency of 37 khz for 60 min (ultrasonic irradiation was accomplished with an elmasonic p ultrasonic clean- ing unit (bath ultrasonic) at a frequency of 37 khz and 100% output power). glutamine solution was added dropingwise to this mixed solution with continuous ultra- sonic effect. immediately, the suspension containing the precursor of zno turned milky white, which indicated



the formation of zno nanoparticles. this was followed by a simple evaporation and drying (hydration/dehydration method) process modified from previous procedures in the literature [27]. the suspension containing zno nano- particles was heated to 70°c for 10 h until complete evaporation of water zno nanoparticles were repeatedly washed several times with ethanol and deionized water to remove ionic impurities and filtered. thereafter, the precipitate was collected by decantation and dried at 100°c overnight. the zno nanoparticles were then annealed in an electric furnace at 300°c, 500°c, or 700° c for 2 h under an air atmosphere and cooled to room temperature naturally. the resulting samples were labeled as zno-g300, zno-g500, and zno-g700.

analytical instruments

zno nanoparticles zno-g300, zno-g500, and zno-g700 were characterized by using different characterization techniques. powder-x-ray diffraction (xrd) patterns of the zno photocatalysts were recorded by a bruker axs d4 endeavor diffractometer using a reflection geometry with fixed divergence slits and cu-k? radiation (? = 0.15418 nm). to determine the particle size and element type, field emission-scanning electron microscope (fe- sem) images and corresponding energy-dispersive (edx) spectroscopy were taken with an fe-sem (jeol jsm-
6700f, japan). transmission versus cm?1 was studied by
ftir model m 2000 midac, u.s.a. ultraviolet diffuse reflec- tance measurement was carried out to measure the band- gap energy, which was recorded with a uv?vis spectro-
photometer (varian cary 100) equipped with a labsphere integrating sphere diffuse reflectance accessory.

photocatalytic degradation

the synthetic wastewater containing maxilon blue dye (grl) using a test of photocatalytic activity for prepared zno nanorods under the illumination of uva light. led uv (a) 365 nm/thorlab, u.s.a., using as a light source of photocatalytic degradation. the incident photon flux measured by uva radiometer, dr honle/germany, was switched on after three minutes. the molecular structure of grl is shown in figure 1. all the experiments were carried out at 25 ± 3°c. the ph of dye solutions was adjusted by adding 0.1 m hno3 or naoh using iq scien- tific experiment ph meter. the solution was continuously stirred for 30 min in a dark environment to reach the adsorption/desorption equilibrium of grl dye over the surface of zno nanorods. at varied time intervals, 3 ml of the dispersion was extracted from the sample and centrifuged at 3500 rpm for 10 min.
the change in concentration of the centrifuged dye solutions was evaluated by measuring the relative




figure 1. molecular structure of maxilon blue dye grl.


intensity of uv–visible absorbance at 605 nm using a uv 1650 spectrometer (shimadzu, japan). the removal rate of photodegradable dye was calculated as ct /c0, where c0 is the initial concentration and ct is the concen- tration of centrifuged grl dye solution (mg/l).
unless otherwise specified, all the experiments were done at natural ph of grl (6.3). the effect of various oper- ational parameters such as calcination temperature (300° c, 500°c, and 700°c), amount of catalyst (0.25–5.00 g/l),
concentration of dye (10–200 mg l?1) and ph (3–10) of
dye solution on the photocatalytic efficiency and rate of dye degradation was studied. moreover, the effect of elec- tron scavengers on photocatalytic degradation was also investigated, and high photocatalytic degradation of maxilon blue dye grl was found at ph 6.3.



3. results and discussion

characterizations of synthesized zno nanorods

xrd was used to investigate the phase and purity of the as-synthesized zno and aid by three types of calcination temperatures. figure 2(a) shows the xrd patterns of the as-synthesized zno the amorphous character has been




figure 2. the xrd diffractogram of zinc oxide nanoparticles at different annealing temperatures (a) as-synthesized, (b) zno- g300, (c) zno-g500, and (d) zno-g700.





figure 3. fe-sem images of zno nanorods (a) as-synthesized, (b) zno-g300, (c) zno-g500, and (d) zno-g700.


indicated to have resulted from the organic glutamine and oxalic acid residues. less intense peaks were found
at the 2? values from 20° to 40°, which attributed to


table 1. edx analysis results of zno nanorods at different annealing temperatures.

zg3 zg5 zg7
weight atomic weight atomic weight atomic
element % % % % % %
o 19.66 48.77 18.46 45.75 16.3 40.4
zn 80.34 51.22 81.54 54.24 83.7 59.56
total 100 100 100 100 100 100


to complement xrd, ftir spectra were performed of zno as-synthesized and annealing samples, and the results are shown in figure 4. it is clear from the results
that the absorption peak between 2344 and 2352 cm?1
indicates the existence of co2 molecules in air [34]. since the measurement was carried out at room temp- erature under air atmosphere, the absorption of h2o from moisture content and co2 from the atmosphere
is unavoidable. the broad absorption peaks at ?3480
and ?1607 cm?1 can be assigned to the presence of hydroxyl groups in the absorbed water (figure 4(a)) these peaks disappear with increasing annealed temp-
eratures (figure 4(b–d)) due to the removal of absorbed water [35,36]. the well-resolved intense and broad trans-
?1

the presence of a minor crystalline phase of zn-gluta-

mission band below ?520 cm

was attributed to the

mine organo–inorganic complexes [26]. after calcina- tions, the characteristic peaks (figure 2(b–d)) can be matched to the hexagonal structure of wurtzite zno detected according to the standardized jcpds card (no. 36–1451) [28,29]. all calculations of crystal size depend on the peak (101) plane. the (101) plane had high purity and strongest line for all studied samples within annealing temperatures. the highest stronger dif- fraction peaks of zno-g500 has been investigated, indi- cating that the shape of zno nanoparticles well crystallized with the annealing temperature [29,30].
the morphology of zno samples was observed by using fe-sem. as shown in figure 3, zno-g300 exhibits as ‘chemical sedimentary rocks’ due to the agglomera- tion of nanoparticles (figure 3(a)), whereas the fe-sem in figure 3(b) and in the inset of figure 3(b) indicate that zno-g300 has a shape of nanorods with some irre- gular composed. figure 3(c,d) and the inset of figure 3(c,
d) show a clearer morphology of zno nanorods (zno- g500 and zno-g700), respectively this is attributed to that the annealing temperature which plays an impor- tant role in determining the structure and morphology of zno the same behavior has been found in previous published works [30–32].
the elemental analysis of the synthesized zno samples were confirmed by edx, which shows the pres- ence of atomic percentages of oxygen and zinc as illus- trated in table 1, with higher concentration of zn, which is attributed to high oxygen vacancies [33].

stretching vibration of zinc–oxygen bond [37,38].
the optical properties of zno samples were examined at room temperature by using uv–vis diffuse reflectance spectra, shown in figure 5. it can be clearly evidence that all samples show an absorption strong edges around 370–380 nm, which can be caused by the intrinsic band-gap absorption of zno, revealing to the electron transitions from the valence band to the conduction band (cb) (o2p?zn3d) [39,40].
optical band-gap energies were determined using the
kubelka–munk function by extrapolation of the linear part





figure 4. ftir spectra of zno nanorods (a) as-synthesized, (b) zno-g300, (c) zno-g500, and (d) zno-g700.





figure. 5. uv–visible absorption spectrum of zno nanoparticles.

of the plot between the (f(r)e1/2) versus the energy of the absorbed light (hv) [41]. the obtained eg values are 3.23, 3.22, and 3.20 ev as the temperature increased from 300°c to 700°c, respectively. compared to the reported values of band-gap energy of bulk zno (eg = 3.37 ev) [42], the optical absorption edge slightly shifted toward red


wavelength, which may be induced by more defects appearing at higher annealing temperatures [43].


effect of different parameters on photocatalytic activity

calcination temperature
calcination temperature has a prominent effect on the efficiency of the prepared photocatalysts therefore, the influence of the calcination temperature on the photoca- talytic activity of irradiated maxilon blue dye grl by uva light was examined. the zno nanoparticles were sub- jected to various calcination temperatures ranging from 300°c to 700°c.
it is clear from the results shown in figure 6(a,b) that the photocatalytic activity of the prepared samples increased with an increase in the calcination tempera- ture from 300°c to 500°c. at 500°c, the photocatalytic efficiency reached the maximum, which is attributed to the change in size and particle morphology of the zno surface [33], or might be due to the enhancement of the crystallization, which is beneficial because it reduces the recombination of photo-generated electrons






figure 6. (a) uv–visible absorbance spectra, (b) percentage of photodegradation removal (%) of decomposed grl dye solution at different annealing temperatures of synthesized zno under uva, (c) uv–visible absorbance spectra with respect to time intervals, and (d) a schematic illustration of grl dye photodegradation by zno annealing at 500°c (zno-g500).



and holes [44]. in addition, with further increase in the calcination temperature from 500°c to 700°c, the photo- catalytic activity decreases. the time-dependent elec- tronic absorption spectrum of maxilon blue dye grl during photoirradiation in the presence of zno-g500 is presented in figure 6(c) the absorption intensity decreases with an increase in the irradiation time.

the intermediate un-degradable organic species, remained in the solution [46].

radical scavenger
during the photocatalytic degradation of maxilon blue grl, both the photo-generated holes and electrons can produce ros. therefore, to further understand the role

besides, no new bands were detected in the uv–vis

of the ros ( oh• , o•2 ?

or h+) involved and to check

region due to the photodegradation process. further-
more, figure 6(d) exhibits the suggested mechanism under uva irradiation for the degradation of grl in the presence of zno-g500 as a photocatalyst for the desired reaction, the energy required to promote an electron (?) from the valance band (vb) to the cb of zno-g500 upon light illumination is equal to or higher

their impact on the photocatalytic degradation of grl
dye under uva light, hole scavengers and radical scaven- gers were added to the reaction of the photocatalytic degradation process. the reaction mechanism of maxilon blue dye photocatalytic degradation through the gener- ation of ros can be described in thefollowing equations:

adsorption

than the band-gap energy. the created photo-excited ?
at the cb of zno-g500 produces radicals such as super-

zno + grl ‹

grl/zno, (1)

? grl/zno + hv ‹ grl/zno(e? + h+ ), (2)

oxide anion o2 due to the interaction with surface
oxygen. at the vb side, active oxygenated species such
as oh radicals are produced by the reaction of either

zno(h+ ) + h2o ‹ oh•

cb
+ h+

vb

, (3)

h2o or ?oh species with h+ forms on the zno surface these steps lead to the photocatalytic degradation and

zno(h+ ) + oh?
zno(e?

‹ oh•
• ?

, (4)

mineralization of the organic pollutant [45].
the mineralization of the maxilon blue dye grl by using different samples of zno photocatalysts was checked with a total organic carbon (toc) analyzer, and the results are depicted in figure 7. the results showed that toc was removed with difficulty after 180 min of irradiation in this time the grl dye comple- tely degraded, while only 18.03%, 29.19%, 48.54%, and 41.34% toc for zno (as synthesized), zno-g300, zno- g500, and zno-g700, respectively, indicating some of




figure 7. effect of annealing temperature on photocatalytic min- eralization of grl dye catalyzed by zno: catalyst amount
1.5 g l?1 ph of solution 6.3 grl dye concentration
(100 mg l?1) and irradiation time (degradation = 180 min).

cb) + o2 ‹ o2 , (5)
oh• + grl ‹ intermediate product
‹ degradation, (6) o•2 ? + grl ‹ intermediate product
‹ degradation. (7)

initially, grl molecules are adsorbed onto the zno surface, after that the suspension of grl/zno is irra- diated by a chosen wavelength, generating cb electron
(e?) and valence band holes (h+) [47]. to further under-
stand the photocatalytic degradation mechanism,
several scavengers were used as the oh• radical scaven-
ger isopropanol (ipa) was added [48], n-phenyl aniline
(dpa) was introduced as the scavenger of o•2 ? [49] and
potassium iodide (ki) was added as a scavenger of both h+ and oh• [50].
the results are shown in figure 8. shows the radical species plays a major role in the photocatalytic degra- dation of grl, the degradation efficiency is expected to decrease greatly. the poorest results were observed with in the presence of ki, which could capture the
reactive species (e.g. both h+ and oh• , more as hydro-
peroxylhoo• radicals) to inhibit the photocatalytic
activity. moreover, the lowest grl dye photocatalytic degradation efficiency suggested indirectly that both
h+ and oh• are considered as a very important reactive
species in the photocatalytic process. on the other hand, compared with ki, photocatalytic degradation in the presence of dpa or ipa still played a vital function,
but was less effective than oh• [51,52].


however, high amount of zno nanoparticles became much easier to aggregate and reduced the light trans- mission [54,55]. furthermore, activated zno may be deactivated through collision with ground-state catalysts as follows:


collision
zno? + zno ‹


zno# + zno, (8)

where zno? and zno# are the activated and deactivated forms of zno, respectively.








figure 8. effect of scavenger concentration on photocatalytic degradation grl dye catalyzed by zno-g500: catalyst amount
1.5 g l?1 ph of solution 6.3 grl dye concentration
(100 mg l?1) and irradiation time (degradation = 60 min).


catalyst loading
the effect of photocatalyst loading on grl removal using zno-g500 photocatalyst was investigated by varying the amount of photocatalyst. it was observed initially that the photodegradation efficiency increased with an increase in the amount of the photocatalyst until a
certain limit up to 1.5 g l?1, after that it slightly decreased
(figure 9).
this phenomenon could be attributed to the increase in active sites with the increase in zno-g500, which is responsible for the enhanced photocatalytic activity [53].
indeed, improvement in the removal efficiency is not obvious with further increase in the zno dosage.





figure 9. effect of catalyst dosage on the photocatalytic degra- dation of grl dye catalyzed by zno-g500: ph of solution 6.3 grl
dye concentration (100 mg l?1) and irradiation time (degra-
dation = 60 min).

ph of solution
the ph of the solution is an important parameter in photocatalytic degradation reactions, because the gen- eration of hydroxyl radicals is considered as a function of ph. therefore, the degradation of dye was studied at different phs of the solution in acid, neutral, and alkaline media, which is shown in figure 10, and indicated that the degradation rate and the photocatalytic removal effi- ciency of grl in a neutral medium are higher than that in an acid or alkaline medium.
the observed trends from figure 10 are clearly related to the electrostatic interactions which can be changed depending on the chemical nature between the sub- strate grl and the photocatalyst zno nanoparticle surface, which depends on the ph point of zero charge (phpzc) and the ph of substrate. comparing the rate of photocatalytic degradation and photodegradation effi- ciency of grl dye at different ph values, we conclude that the degradation seems to be slow in both acidic and basic media. however, the highest degradation of the grl dye occurs at ph = 6.5.
thus, when the ph values are below the phpzc, the cat- alyst particles are protonated and become positively charged [56,57]. however, when the ph values are above the phpzc, the catalyst particles are deprotonated and become negatively charged [58,59]. the phpzc of zno nanoparticles is about 9. additionally, the grl dye has a neutral ph. therefore at acidic ph, both zno nanoparticles surface and grl dye are positively charged and the same polarity of charge results in an electrostatic repulsion between them, which reduces the adsorption on the cat- alyst surface. at ph between 6.5 and 7.5, the grl has a neutral charge, whereas the zno photocatalyst has a nega- tive charge, favoring the adsorption and it is responsible for the high degradation. at ph > 8.5, both grl and zno are negatively charged, so the repulsive forces between the catalyst and the molecule are developed.

initial dye concentration
the dependence of photocatalytic degradation effi- ciency on the initial concentration of maxilon blue dye was investigated the experiment was repeated at a range of initial dye concentration from 10 to





figure 10. influence of initial solution ph on the photocatalytic degradation of grl dye catalyzed by zno-g500: catalyst suspended =
1.5 g l?1 grl dye concentration (100 mg l?1) and irradiation time (60 min).


200 mg l?1 (figure 11(a)). high values of (r2) were obtained from the nonlinear line relationship of ct/c0 versus irradiation time t. this behavior of photocatalytic degradation indicates a first-order expression up to an initial concentration of grl dye.
data on the rate constant obtained from figure 11(a) were then fitted to the langmuir–hinshelwood (l–h) kin- etics rate model, which has been applied to analyze the concentration of pollutants as a function of the initial rates of photocatalytic degradation [57,60,61]. the rate law is shown in the following equation:

that the degradation of grl occurred mainly on the surface of zno and fitted well to the l–h model. the values of k and k, determined from the nonlinear expression of the plot, are 4.194 × 103 g l?1 min?1 and
8.93 × 10?5 l g?1, respectively.
based on the results in figure 11(a), the photocatalytic degradation efficiency is very high at low concentrations of the maxilon blue dye, and then, as the dye concen- tration increases, it gradually decreases. this might be attributed to a competition of adsorption between dye molecules (e.g. grl) and dissolved o2 into the catalyst
surface (e.g. zno). as o2 molecules are the electron accep-

dc klkadsc0

r = dt = 1


kadsc0

. (9)

tors in the photocatalytic reaction, therefore, lesser the o2
adsorbed than the dye on the catalyst surface, lesser is the

the applicability of the l–h equation for degradation has been confirmed by the nonlinear plot model (r2 of 0.9359), obtained for rate of photocatalytic degradation versus initial concentration (figure 11(b)). this indicates

degradation efficiency as well as the rate constant [11]. another possible cause for such results is the effect of uv-screening of the dye itself, because a very low amount of uv may be absorbed by the zno nanoparticles






figure 11. (a) kinetics of nonlinear fit, and (b) l–h model of photocatalytic degradation of grl dye catalyzed by zno-g500: catalyst suspended = 1.5 g l?1 ph 6.3 irradiation time (60 min) and l.i. 2 mw cm?2.





figure 12. the reusability of zno-g500 photocatalyst: catalyst suspended = 1.5 g l?1, grl dye concentration (100 mg l?1), ph
of solution 6.5, and irradiation time (60 min).


at a high dye concentration, which reduces the photoca- talytic efficiency of the surface reaction [52].


3.2.6 reusability of catalyst
to study the stability of zno-g500 photocatalyst, zno nanoparticles were recovered from the reaction mixture by filtration and reused six times under similar
reaction conditions: the usage of zno-g500 (1.5 g l?1),
grl dye concentration (100 mg l?1), ph of the solution (6.5), and irradiation time (60 min). after the completion
of the first run of the photocatalytic degradation exper- iment, zno-g500 was collected through filtration, washed several times using deionized water, then dried for 4 h at 100°c, and the product was used in the next photocatalytic degradation experiment. the results of the first experiment and five repeated experiments are shown in figure 12. it was observed that after reuse, zno-g500 nanoparticles showed lower photocatalytic activity: the photodegradation efficiency dropingped from 97.99% of the 1st use to 82.39% of the 6th repeated use. this result illustrates that the surface of zno-g500 nanoparticles showed very good stability.


4. conclusion

in this work, a green precursor-based economical and convenient method for preparing zno nanorods by sonochemical/hydration–dehydration method using glu- tamine as a biotemplate was investigated. the effects of annealing temperature on zno nanoparticles with respect to the morphological characteristics were inves- tigated. xrd results confirmed that the zno nanoparti- cles have pure hexagonal wurtzite structure. fe-sem


micrographs show that the particle size was temperature dependent therefore, the average crystallite size increased with increasing calcination temperature for the zno samples. the best photocatalytic performance in the degradation of grl was found to be zno-g500
> zno-g700 > zno-g300 > zno as-synthesized, respect- ively. photodegradation of grl dye by zno nanoparticles was studied thoroughly and the effect of various par- ameters such as effect of solution ph, catalyst loading, and initial dye concentration was also investigated. the applicability of the l–h kinetic model reveals that the degradation of maxilon blue dye occurs mainly on the surface of the photocatalyst.


acknowledgements

the authors would like to thank university of northampton, uk, for the material characterizations.


disclosure statement

no potential conflict of interest was reported by the authors.


orcid

ayad f. alkaim http://orcid.org/0000-0003-3459-4583


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