Graphene Oxide Based Metallic Nanoparticlesand their Some Biological and EnvironmentalApplication

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Graphene Oxide Based Metallic Nanoparticles and their Some Biological and Environmental Application

Article in Current Drug Metabolism · October 2017

DOI: 10.2174/1389200218666171016100507

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Current Drug Metabolism

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REVIEW

^ARTICLE

Graphene Oxide Based Metallic Nanoparticles and their Some Biological and Environmental Application

Aftab Aslam P. Khan

^1,2*

, Anish Khan

^1,2

, Abdullah M. Asiri

^1,2

, Ghulam Md. Ashraf

³

and Basma G. Alhogbia

²

1Center of Excellence for Advanced Materials Research, King Abdulaziz University, Jeddah 21589, Saudi Arabia; ²Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia; ³King Fahd Medical Research Center, King Abdulaziz University, Jeddah 21589, Saudi Arabia

A R T I C L E H I S T O R Y Received: April 06, 2017 Revised: July 29, 2017 Accepted: October 06, 2017

DOI:

10.2174/1389200218666171016100507

Abstract: Background:Recently the decoration of graphene with metallic nanoparticles by a synchronized reduction of graphene oxide (GO) and synthesis of metallic nanoparticles has gained momentum. Metal-decorated carbon substrates, for example, carbon nanotubes and graphene oxide have been of interest to the scientific group all through the past three decades on account of different potential applications. The utilization of graphene oxide as the nano scale substrates for the formation of nanocomposites with metal oxides is a novel thought to acquire a hybrid which would show both the properties of GO as an interesting paper-shape material and the elements of single nanosized metal particles.

Methods:Graphene is a carbon allotrope of sp2 hybridized carbon atoms in a honeycomb lattice. It has attracted unique properties and potential applications. It has been synthesized and modified through various methods, and composites have been made with other nanomaterials, such as metals, metal oxides, and some complex oxides.

Results:Grapheme-metal oxide composites are gaining attention as a viable alternative to boost the efficiency of various catalytic, storage reactions in energy conversion, anticancer and drug delivery applications. Nevertheless, by combining the superior physical/chemical properties of GO themselves and the versatile nanomaterials that can decorate with GO, GO based materials have a bright future in the anticancer, drug delivery, energy, and environmental applications.

Conclusion:This review article has described the recent publications in the development of Decoration of Graphene Oxide such as metals, metal oxides and their nanocomposites based materials. We anticipate this active field will continue growing rapidly, leading eventually to a variety of mature materials and devices that would benefit the society. Finally, the applications of composites are at their initial stages. They need to be studied systematically from both theoretical and experimental aspects.

Keywords: Graphene oxide, metallic nanoparticles, decoration, pulsed laser ablation, drug delivery, photocatalytic degradation.

1. INTRODUCTION

Nanotechnology is a rising field of present day science and innovation which helps us in improving human life to be better.

Nanocomposites made of metal decorated carbon substrates including graphene oxide and other materials have been the theme of late research enthusiasm for the field of nanoscience and engineering.

Graphene, a standout amongst the most intriguing materials in materials science, has been broadly examined inferable from its special electronic, thermal, mechanical, and chemical properties and potential specialized applications [1-3]. Nanoparticles (NPs) with at least one measurements of size 100 nm or less have exhibited their benefits over their mass partners because of their extraordinary and interesting properties [4, 5]. A few sorts of chemical, physical, biological or combination of these methods have been exploited for the synthesis of different kinds of NPs [6-10].

Graphite oxide sheets, now called graphene oxide is the result of chemical exfoliation of graphite that has been known for over a century [11-13]. It is commonly synthesized by reacting graphite powders with strong oxidizing agents, for example, KMnO₄ in concentrated sulfuric acid [14, 15]. The oxidation of graphite separates the broadened two-dimensional (2D)- conjugation of the stacked graphene sheets into nanoscale graphitic sp² spaces encompassed by disordered, highly oxidized sp³ domains and also defects of carbon opportunities. The subsequent GO sheets are derivatized via

*Address correspondence to this author at the Center of Excellence for Advanced Materials Research, King Abdulaziz University, Jeddah 21589, Saudi Arabia; Tel: (02) 6952293; E-mail: [email protected]

carboxylic acid at the edges, and phenol, hydroxyl and epoxide groups mainly at the basal plane (Fig. 1) [16, 17].

Chemically changed graphene or graphene’s subordinates, for example, GO, have been strongly considered as of late for some applications [18]. They have been utilized as a part of nanocomposites’ synthesis for applications such as transparent conducting films, catalysis, fuel cell, light energy conversion, and sensing [19- 23]. As per Bananni et al. graphene oxide is the oxidized type of graphene sheet with oxygen functional groups, for example, hydroxyl, peroxy, carbonyl, carboxyl, aldehyde and epoxy [24, 25].

As of now, GO is normally synthesized utilizing the already speci- fied altered Hummers method which includes the chemical exfoliation of graphite either thermally or ultrasonically within the sight of strong acids and oxidizing agents [26-31]. This covalent functionalization brings about the disruption of the sp² network forming sp³ bonds rendering GO as a phenomenal electrical insulator [32, 33]

On the other hand, the oxygen functional groups on the basal plane and edges enable the dispersibility of GO in polar solvents, for example, water [34, 35].

Additionally, graphene sheets decorated with metal oxide NPs consolidate the exceptional properties of them and might bring about some specific properties on account of the synergetic effect between them. The advancement of graphene-based composites gives a vital turning point to enhance the application execution of metal oxide nanomaterials in various fields, for example, energy harvesting, conversion and storage devices, photovoltaic gadgets, photocatalysis, and so on. On the grounds that the hybrids have adaptable and tailor-made properties with exhibitions better than

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Graphene Oxide Based Metallic Nanoparticles Current Drug Metabolism, 2017, Vol. 18, No. 11 1021

those of the individual oxide nanomaterials, significant endeavors for decorating graphene with metal oxides NPs [36-38] have recently been reported.

In this review article, an exertion has been made to depict a concise outline of the current research concentrated on the decoration of graphene oxide with metal and metal oxide nanocomposites, and the investigation of their properties and a few applications, concentrating on the current advancements of NPs synthesized by this method has additionally been summarized in the review. At last, we end up with discussion on the difficulties in future development of the class of nanocomposites.

2. GRAPHENE OXIDE AS LAYOUT FOR METAL NANOPARTICLE SYNTHESIS

A few strategies for the synchronous synthesis and deposition of metal nanoparticles on the surface of carbon substrates including GO have been investigated. Then again, there have been reports of discrete synthesis of metal nanoparticles made by ensuing deposition on carbon substrates. This segment tries to review literature on the thermal, photo reduction, chemical reduction, sonication, electrochemical, and microwave methods used to deposit metal nanoparticles on carbon substrates with graphene oxide substrate and metal as the fundamental focus. The binding or loading of metal and metal oxide NPs on graphene for the preparation of graphene-based nanocomposites is for the most part acknowledged in two distinctive ways (Fig. 2): one is post immobilization like ex situ hybridization; another option is in situ binding/ crystallization. Post immobilization includes blending of discrete solutions of graphene nanosheets and pre-synthesized NPs. Before mixing, the NPs as well as graphene sheets are surface functionalized to improve the process ability of the subsequent items. The conjugated graphene sheets can promptly be functionalized by non-covalent stacking or covalent C-C coupling reactions. The functionalization of graphene and additionally NPs significantly upgrades their solvency and henceforth widens the opportunities for the preparation of graphene-based composites. In the present review in situ strategies for the planning of metal and metal oxide decorated graphene-based nanocomposites will be discussed in some details. Readers keen in details of the post immobilization methods (e.g. materials utilized for the functionalization and the planning of functionalized graphene based metal nanocomposites) can counsel great reviews by Yang or Shi and co-workers [39-43].

Techniques for the preparation of graphene based metal and metal oxide nanocomposites by in situ chemical reduction of metal precursors, for example, HAuCl4, AgNO3, K2PtCl4, and H2PdCl6

with reductants like hydrazine hydrate, amines, and NaBH4 are more typical and generally applied [44]. For case, HRG/Au nanocomposites were set up by the reduction of HAuCl4 with NaBH4

[45] and graphene-based bimetallic HRG/Pt/Pd nanocomposites were incorporated by in situ reduction of H2PdCl4 and K2PtCl4 with HCOOH and ascorbic acid [46]. Apart from metallic and bimetallic NPs, the composites of metal oxides with graphene have been synthesized by in situ chemical reduction [47, 48]. Kim et al., arranged HRG/Co3O4 nanocomposites as anode materials, by the reduction

of GO and cobalt acetate in deionized water (DI) with NH4OH and hydrazine as reductants [49].

Apart from this, microwave irradiation (MWI) is generally connected for the synthesis of graphene-based nanocomposites [50, 51]. The primary preferred standpoint of MWI over other conventional heating method is the quick and uniform heating of the reaction mixture. Microwave irradiation is a quick and easy technique to give energy for chemical reactions. Yu and co-workers first synthesized uniform nanoparticles of Pt in a colloidal blend stabilized by N-Vinylpyrrolidone in 1999 [52]. In this trial, the nanoparticles were additionally synthesized using conventional heating mantle and oil bath. The latter procedures brought about a wide distribution of nanoparticles because of the uneven heating of the mass solution.

Therefore, microwave-helped synthesis offers more focal points over consistent heating. Microwaves can enter solution mixture bringing about uniform heating, shorter crystallization time in addi- tion to large scale homogeneous nucleation [53]. A year later, Ro- gach et al., announced the microwave synthesis of CdSe quantum dots stabilized by citrate ligands [54]. The particle size of their nanoparticles was ~5 nm. These nanocrystals were later coated with silica to form spheres which can be utilized for building semiconductor composites. A part from this, microwave helped synthesis and metal nanoparticles decoration of carbon supported an extensive achievement in the late years [55-64].

Microwave-helped Ag nanoparticles synthesis and deposition on graphene oxide substrate was later researched by Han et al. In their approach, ecologically well-disposed starch was utilized as both a stabilizing and a reducing agent. Moreover, after, decoration with Ag nanoparticles, there was upgrade of the Raman signal of GO showing that this nano-hybrid can be utilized as Surface En- hance Raman Scattering (SERS) substrate for identification of low Raman active molecules [55]. Because of the various advantages offered by microwave irradiation for the synthesis of metal nanoparticles, and the horde of applications and potential uses of these nanoparticles, the synthesis of gold decorated graphene oxide was effectively attempted by Jasuja et al., from Kansas State Uni- versity [56]. Also, this method enhanced the chemical synthesis of nanoparticles without the use of harmful chemical or the need to expel harmful byproducts from gold decorated graphene oxide nano-hybrid.

Supporting the metal nano particles on the graphene sheets could keep the formation of stacked graphite structure in light of the fact that the metal nano particles can go about as spacer to incre- ment the surface area of the nanoparticle graphene composites [65- 77]. These materials may have promising potential application in catalysis, fuel cells, chemical sensors, and hydrogen storage. Great dispersion of the metal nanocrystal as on the graphene sheets can be accomplished by the concurrent reduction of the metal salts and GO during the MWI process [78]. Fig. (3) compares the TEM images of the Pd/Graphene sample prepared by mixing independently prepared Pd nanoparticles under MWI for 20-25s. It is evident that the straight forward physical mixing of the nanoparticle and graphene sheet brings about a critical total of the metal nanoparticle with very poor dispersion on the graphene sheets.

Fig. (1). Structural model and microstructures of GO sheets.

Oxidation Reduction

O OH O OH HO

OH O HO

O

HO O

O

OH OH

OH O

O HO

O HO O O

OH O

O OH

O OH O OH HO

OH O

HO O

OH O

HO O HO O

O OH O

O OH

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1022 Current Drug Metabolism, 2017, Vol. 18, No. 11 Khan et al.

Due to the several benefits offered by Pulsed Laser Ablation in Liquids for the synthesis of Ligand-free metal nanoparticles (MNPs), and the horde of applications and potential uses of these nanoparticles, the synthesis of gold decorated graphene oxide was effectively embraced as indicated by G.M.V. et al., from Univer- sität Jaume, Spain [79]. Ligand-free MNPs have been effectively arranged by laser irradiation utilizing an optional and simple top- down procedure that satisfies the standards of green chemistry [80, 81]. Pulsed Laser Ablation in Liquids is depends on a focused pulsed laser beam light on top of the surface of solid target bounded through any type of liquid or colloid [82-85]. As that ligand-free nanoparticles of gold exhibit an enhanced specific surface move- ment because the nonappearance of ligands in the surfaceand the particles might be held on the surface of sheets of graphene by the mix of various impacts:

• A electrostatic interactions among the NPs and graphene quick towards a strong immobilization.

• The -electron aromatic coordination found graphene and its byproducts interacts with the d-orbitals of the metal nanoparticles.

• The particular spreading of NPs at the deformities obatin in graphene.

Decoration of NPs of gold ligand free formed separately by Pulsed Laser Ablation in Liquids and then mixed with graphene derivatives has been accounted for through different re- searcher.Recent report by G.M.V. et al. was concentrated on gener- ating gold nanoparticles ligand-free anchored to sheets of GO in a single reaction stage. The effect of the femtosecond based on radiation method to the control for the production of gold nanoparticle’s Fig. (2). Schematic illustration of the binding mechanisms of nanoparticles onto HRG sheets [108]. (Copyright^© 2015, Royal Society of Chemistry).

Fig. (3). Images of TEM of graphene sheets containing Pd nanoparticles via chemically converted (a,b,c) and (d,e,f) reduction of grapheme oxide and Pd nitrate using hydrazine hydrate with the process of MWI. (Copyright^© 2009, Royal Society of Chemistry).

Organic Ligands, Reduction Polymers or surfactants etc.

ex-situbinding of Nanoparticles

functionalizationPre- Functionalized HRG SHEETS HRG SHEETS Pre-synthesized

Nanoparticles (NPs)

Pre-synthesized Nanoparticles (NPs) Mixing

HRG/NPs Composites

densityLow

NPS NPS NPS

NPS NPS

Functionalized HRG/NPs Composites

NPS NPS NPS

NPS NPS

Graphene oxide Sheets

densityHigh

NPS NPS NPS NPS

NPS NPS NPS NPS NPS

HRG/NPs Composites

HOOC

COOH COOH

COOH OHOOC

HO HOOC

HO O OH

O O OH

HOOC OH COOH O OH

OHOOC HO HOOC

O

HO HO

COOHOH COOH

COOH COOH

HO O OHO O

Exfoliated graphene oxide sheets Metal salts

In-situbinding of Nanoparticles

In-situ Reduction

(a) (b) (c)

500 nm 100nm 50nm

(d) (e) (f)

500 nm 100nm 50nm

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ligand-free in an environment packed with sheets of GO has been examined. Through this point, gold nanoparticle’s were formed in two distinctive fluid situations for correlation determinations:

one is deionized water another one is a homogeneous suspension of GO. Our outcomes show that one is conceivable toward make without ligand metal nanoparticles straight forwardly secured to sheets of GO in a only reaction path. This strategy has been demonstrated towards give a compelling approach to get graphene metal assem- blies that could possibly be utilized as a part of a few applications where undesirable cross synthetic effects should be kept away from.

Readers interested in details of the Laser synthesis of AuNPs utilizing water as dissolvable and immobilized on GO can consult outstanding report by Gladys Mínguez-Vega and coworkers [79]. Util- izing PLAL, G.M.V. et al. have decorated sheets GO with ligand- free gold nanoparticle in an viable and only one step reaction.The strategy of laser-based reasons a slight diminishment of GO yet stays away from the utilization of supplementary chemicals that can modify the properties of Au nanoparticles. The light of a Au circle containing a grapheme oxide material in water prompts to the quick immobilization of produced ligand-free gold nanoparticle on the surface of graphene. As per the examining set-up in Fig. (4), the light of laser radiation interfaces through the suspension of GO already achieving the gold plate.

To set up any impact from the laser radiation on the graphene material, the AuNPs were set up in two diverse fluid conditions, i.e.

deionized water and a graphene oxide suspension in water. Exami- nation of the after effects of both tests proposes that graphene oxide has an impact on the AuNP arrangement and in graphene oxide itself by:

• Diminishing the particle size as normal.

• The particles immobilizing on surface of graphene.

• Heterogeneously distributing the tied down gold nanoparticles at the wrinkles of graphene.

• Somewhat decreasing the graphene oxide.

Considering already announced results, comparison of gold nanoparticles tied down onto graphene acquired by chemical meth-

ods and laser ablation. Authors watched that chemical strategies permit a superior control of the extent of scattering of nanoparticles and deliver a total diminishment of GO [86, 87] When utilizing laser ablation for the synthesis of gold nanoparticles, the GO is just somewhat decreased and the inalienable properties are safeguarded.

The graphene goes about as a topping specialist and diminishes the size of the nanoparticles in examination with the development of nanoparticles utilizing water. Authors trust that the straight for- wardness of this technique for AuNPs/GO synthesis may arouse future advancements in the field of materials science.

3. APPLICATION 3.1. Biological Applications

Graphene and graphene-based materials have extraordinary potential in different biomedical applications [88], as demonstrated by the quantity of publications available. A few reviews have focused on biomedical uses of graphene, including drug / gene delivery, imaging, antibacterial and anti-cancer activities [89-92]. Various inorganic nanoparticles (Au, Ag, Pt, Cu, Fe3O4, QDs, ZnO, SiO2, TiO2,etc.) decorated on graphene are helpful for multimodal imaging and thera- peutic applications. Graphene-Fe3O4 conjugates have great magnetic and optical properties thus, utilized as a part of biomedicine. Li et al., proposed a novel nanocarrier in the light of Fe3O4-graphene nanocomposite for a successful drug delivery and pH-responsive discharge framework for cancer treatment [93]. A revealed cross breeds of superparamagnetic graphene oxide-Fe3O4 nanoparticles (GO-Fe3O4) were linked in magnetic resonance imaging (MRI), natural division, and hyperthermia therapy [94]. A detailed conjugation of doxorubicin (DXR) and GO-Fe3O4 hybrids is shown in Fig. (5).

The loading amount of doxorubicin on GO-Fe3O4 was deter- mined in various initial doxorubicin concentrations as appeared in Fig. (6). GO-Fe3O4 hybrid was loaded with anti-cancer drug doxorubicin with a high loading capacity up to 1.08 mg mg^-1, while the amount of doxorubicin loaded on GO was achieved 2.35 mg mg^-1 due to p-p stacking and the hydrogen bonding interaction between GO and doxorubicin both assumed as roles in the high loading of doxorubicin on GO [95].

Be that as it may, Yang et al., [96] revealed may be a most en- couraging superparamagnetic manganese ferrite (MnFe2O4) depos- ited on graphene oxide, examined using as a magnetic resonance imaging, photothermal therapy and drug delivery. Moreover, the drug delivery aspect of GO/MnFe2O4/DOX, in light of the way that DOX acts as a model drug to analyze drug loading and release properties of GO/MnFe2O4, is presented herein. The loading amount of DOX on GO/MnFe2O4hybrid was obtained 339 mg^-1. It is essen- tial in application because the microenvironments in cancerous tissue and intracellular lysosomes and endosomes are acidic, which trigger the drug release from the carriers [97, 98]. In the interim, the insignificant drug spillage from the delivery vehicles under typical physiological conditions creates minimized side-effects to normal organs. The in vitro chemotherapic adequacy of GO/MnFe2O4/ DOX was assessed by quantifying the cell viability of HeLa cells using MTT assays. The release of DOX from the nanohybrids can be triggered by pH and NIR light. In vitro cancer cells therapy

HOOC HOOC

HOOC HOOCCOOH

COOH

HOOC COOH

COOH

HOOC

HOOC HOOC

HOOC HOOCCOOH

COOH HOOC COOH

COOH

HOOC

HOOC HOOC

HOOC

HOOCCOOHCOOH

COOH HOOC COOH

HOOC HO

OH

O

HO OH

O

HO OH

Fe /Fe³⁺ ²⁺ O

NaOH

Fe₃O₄

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experiments by joining PTT and chemotherapy utilizing GO/MnFe2O4/DOX, demonstrated a synergistic effect for cancer cell killing. Moreover, the GO/MnFe2O4nanohybrids with various functionalities are exceptionally useful for applications in bio- imaging and high viability treatment of tumors. As of late, Zhang et al., [99] report a magnetic targeting nanoparticle in view of hollow Fe3O4-GO which wasdeveloped as a potential tumor targeting drug carrier. The drug loading and releasing test showed that the acquired Fe3O4-GO has a good loading capacity of 0.41 mg¹ for 5- FU. The CCK-8 assays of CMEC viability showed that the hollow Fe3O4-GO nanocarriers do not statistically exhibit toxicity with the increasing concentration. Zhao et al., [100] portrayed a GO wrapped Au nanoparticle for intracellular Raman imaging and drug delivery. Anticancer drug DOX was joined onto the nanoparticle surface through noncovalent interactions, and was delivered into HeLa cells for chemotherapy. A novel nano-hybrid consisting of AuNPs and nano-size GO (NGO), indicated as Au^@NGO, in a 3-D morphology by wrapping NGO sheets onto the surface of AuNPs through a one-step synthesis is shown in Fig. (7).

Some of its remarkable accomplishments are high viewpoint proportion Au nanostar/GO hybrids, direct growth of Au rods on graphene thin films, and the uses of GO hybrids for Raman identi-

fication of folic acid [101-103]. Graphene and its subsidiaries, for example, reduced graphene oxide (rGO), which have been utilized as substrates for the attachment of NPs and immobilization of drug molecules for ultrasensitive SERS recognition and controlled drug delivery applications [104-106]. Reduced graphene oxide-gold nanostar (rGO-NS) nanocomposites utilized as active SERS materials for anticancer drug, DOX loading and discharge [107]. The synthesis of these rGO-NS nanocomposites is exhibited schemati- cally in Fig. (8). First, Au NPs were synthesized on the rGO colloidal solution by including Au salt and the reducing agent, sodium citrate. Quickly, different amounts of the as-prepared rGO-NP seed solution were mixed with Au and Ag salts and ascorbic acid to form rGO-NS nanocomposites. Aromatic Raman active molecules for example, mercaptobenzoic acid crystal violet, and doxorubicin indicated particular interactions and improved sensitivity with rGO- NS nanocomposites during Raman estimations under 785 nm laser excitation. The most grounded SERS intensity for rGO-NS over either bare Au NS or rGO-NP seed was ascribed to strong electro- magnetic improvement and nanoantenna effect. The authors have further shown that DOX discharge could be checked by SERS shown in Fig. (9). The SERS estimations of rGO-NP-DOX solution demonstrated that ca. 90 % of the SERS signal was kept up at pH 7.4, while just 9 and 18 % were held for pH 4.0 and 6.0, separately.

The extra DOX released from rGO-NS under acidic conditions can be attributed to the pH-dependent - stacking interaction between DOX and the aromatic domains of rGO. Moreover, SERS uses of rGO-NS to probe DOX loading and pH-dependent release are effectively illustrated, indicating promising potential for drug delivery and chemotherapy. Readers interested in the details of the Graphene based metal and metal oxide nanocomposites combination and their applications can consult amazing reviews in the journal of materials chemistry A [108].

A promising MRI T2 contrast agent, graphene oxide decorated with MnFe2O4 nanoparticles was set up through a simple smaller mini-emulsion and solvent evaporation process [109]. This graphene-based composite material with 14 nm MnFe2O4nanoparticles indicates high T2 unwinding time with relaxivity reading of 256.2 (mM Fe)^-1 s^-1 and the PEGylated type of the composite having enhanced biocompatibility and physiological stability [110-112].

Chen et al., [113] detailed that the created composites of ami- nodextran-covered Fe3O4NPs and GO were productive for cell MRI. As shown in Fig. (10), examination demonstrated in vivo that the internalization of Fe3O4-GO composites had no impact on the cell feasibility and multiplication.

Contrasted with the exposed Fe3O4 NPs, the Fe3O4-GO composites show an altogether enhanced T2 weighted MRI differentia- tion, which is clarified by the way that the Fe3O4 NPs framed bring about an extensive improved T2 relaxivity.

3.2. Environmental Application

In several decades, destructive synthetic mixes have turned into the primary driver of water contamination. For instance, natural colors are frequently released in wastewater without adequate treatment. Fast and helpful removal of natural colors from wastewater has been a testing issue confronted by researchers. For example, graphene-based manganese oxide composites were connected as adsorbent materials [114]. The mix of graphene sheets and MnO2

NPs fills the need of water purification. As of late, metal ions scav- enging utilizations of HRG/MnO2 nanocomposites have been exhibited by Sreeprasad et al., taking Hg(II) as a model pollutant [115]. HRG/Fe3O4 nanocomposites have have been utilized as ad- sorbents for the expulsion of overwhelming metals and different contaminants from nature utilizing their magnetic properties, high surface-to volume proportion and short dispersion rate by the support of graphene [116, 117].

A few reviews have been published, including a report of Zhang et al., on the synthesis of HRG/Fe3O4 nanocomposites and 2.4

2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4

0.2 0.10 0.20 0.30 0.40 0.50 A

B

Initial DXR Conc. (mg ml^-1)

Loading of DXR (mg ml

-1

)

< 400nm

Dox

Nano-size GO (NGO) HAuCl4

NaHB4

Raman

Bio-imaging by SERS

Chemotherapy Cancer Cell

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their application in the elimination of tetracycline [118]. Chandra et al., portrayed the synthesis of HRG/Fe3O4 nanocomposites comprising Fe3O4 NPs (10 nm), which demonstrated a high binding limit with respect to As (III) and As (V) in drinking water [119]. An HRG/Fe3O4 hybrid prepared by Geng et al., exhibited outstanding

adsorption execution for a progression of colors, for example, RhB, R6G, AB92, OII, MG and NC [120]. Likewise, the material can be quickly isolated from water because of the proximity of magnetic Fe3O4 NPs, and proficiently recovered and used by means of straight- forward annealing treatment under direct conditions. Also, graphene- HAuCl4

Sodium Citrate

HAuCl4 AgNO3 ,

Ascorbic Acid DOX

Probing Drug Delivery by SERS

785 nm

Graphene oxide Au NP Au NS* Doxorubicin (DOX)

(a) 1500 1000 500

0 Initial pH = 7.4pH = 6.0pH= 4.0 300 400 500 600 700 Roman Shift (cm^-1)

SERS Intensity (a.u.)

(b)

Initial

After buffer wash pH = 7.4

pH = 6.0 pH = 4.0

GO

control 5mmgmL^-1 10mgmL^-1 20mgmL^-1 40mgmL^-1

control 10³ cells 10⁴ cells 10⁵ cells 10⁶ cells MRI

Cellular uptake AMD-Fe_{3 4}O NPs

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based iron oxide nanocomposites including HRG/Fe3O4 and HRG/Fe₂O₄ have exhibited brilliant adsorption capacity to tie other heavy metals and organic dyes, for example, chromium, lead, cobalt, neutral red, methylene blue etc. [121-124]. A ternary composite of HRG/Fe₃O₄/TiO₂ has been reported, which displayed high selectivity and limit in catching phosphopeptides [125]. In another study, reduced graphene oxide based silver nanoparticle containing composite hydrogel was proved to be a highly efficient dye catalyst for wastewater treatment [126]. The charge exchange mechanism in the RGO/PEI/Ag nanocomposite among photocatalytic process is shown in Fig. (11). With the photocatalysis reaction, dye molecules could be exchanged from the solution to the composite’s surface and could be adsorbed with counterbalanced face-to-face orientation via- conjugation amongst RhB, MB and aromatic regions of the graphene [127]. At the point when UV irradiation was connected to the surface of RGO/PEI/Ag nanocomposite, the photo-excited electrons could rapidly infuse to graphene sheets and after that responded with adsorbed O₂ atoms on the graphene to create O2

/ O2

2 radicals [128].

Along these lines, the readied composite could create more electrons and holes, and produce more superoxide anions and additionally per- oxide species [129]. As the consequence of the above creation, dyes are divided into H2O, CO2 and other elements.

Due to the process of electron transfer, charge recombination is suppressed in RGO/PEI/Ag composite and hence largely enhances the efficiency of photocatalytic properties.

CONCLUSION

This review article has described the recent publications in the development of Decoration of Graphene Oxide such as metals, metal oxides and their nanocomposites based materials. Graphene is a carbon allotrope comprising a densely packed atomically thin layer of sp2 hybridized carbon atoms in a honeycomb lattice. It has attracted unique properties and potential applications. It has been synthesized and modified through various methods, and composites have been made with other nanomaterials, such as metals, metal oxides, and some complex oxides. Among them, grapheme-metal oxide composites are gaining attention as a viable alternative to boost the efficiency of various catalytic and storage reactions in energy conversion applications. Nevertheless, by combining the superior physical/chemical properties of GO themselves and the versatile nanomaterials that can decorate with GO, GO based materials have a bright future in the energy, environmental and drug delivery applications. We anticipate this active field will continue growing rapidly, leading eventually to a variety of mature materials and devices that would benefit the society. Finally, the applications of composites are at their initial stages. They need to be studied systematically from both theoretical and experimental aspects.

CONSENT FOR PUBLICATION Not applicable.

CONFLICT OF INTEREST

The authors declare no conflict of interest, financial or other- wise.

ACKNOWLEDGEMENTS Declared none.

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