Utilization of plastic wastes for synthesis of carbon microspheres: A template fornano crystalline copper (II) oxide hollow spheres
Sandesh Y. Sawant1, Rajesh S. Somani1, Sangita S. Sharma2 and Hari. C. Bajaj1,*1 Discipline of Inorganic Materials and Catalysis, Central Salt & Marine Chemicals Research Institute,Council of Scientific & Industrial Research (CSIR), G. B. Marg, Bhavnagar 364002, Gujarat, India
2 Department of Chemistry, Hemchandracharya North Gujarat University, Patan, Gujarat, India.
e-mail: hcbajaj@csmcri.org; Tel: +91 278 2471793; Fax: +91 278 2567562

Abstract
Catalyst and solvent free single step approach for the synthesis of carbon spheres using various municipal plastic wastes
under autogenic pressure is presented. The obtained carbon spheres have been characterized with different microscopic
and spectroscopic techniques. The microscopic analysis showed formation of carbon microspheres having diameters of
1-8 µm. Among the different types of plastic wastes studied, only polyethylene, polypropylene and polyacrylate could beconverted into carbon spheres with 100% purity whereas the carbon particles with irregular shape was observed in caseof other plastic wastes. The absence of catalyst makes the carbon spheres free from metal impurities and avoids thefurther purification process. The synthesis of carbon spheres from plastic wastes proceeds with the formation aromatichydrocarbons. The CuO hollow spheres of wall thickness of ~130 nm have been prepared using plastic waste derived
carbon spheres as template material under ultra-sonic treatment.
Keywords: Plastic wastes; Carbon spheres; CuO hollow spheres

1. Introduction
In the recent years, enormous amounts ofplastic wastes have been generated due to increased
usage, demand and production of plastic materials.
Recycling of the waste material not only helps thegeneration of new resources but also reduces
environmental pollution [1]. Most of the plastic materials
which come to the market are recyclable but there arelots of technical as well as economical problems attachedwith recycling [2]. The difficulties associated with theseparation and sorting of plastic wastes is the biggest
problem with their recycling. The cost effective plastic
materials has been recycled whereas other plastic
wastes are either disposed by land filling or incinerated[3], which again creates the environmental issue due toemission of toxic pollutants.
Over the past decade carbon spheres havebeen attracting the interest of researcher community due
to their interesting physicochemical properties andapplicability as reinforcement materials for rubber [4],supports for catalysts [5], lubricating materials and in fuelcells or secondary lithium ion batteries [6]. Manytechniques such as chemical vapor deposition,
solvothermal synthesis [7], carbonization [8] and arcdischarge [9] have been employed for the production ofcarbon spheres. Many of them utilize the chemical
reagent as carbon feed stock and metal as
catalyst/reducing agent. One of the main disadvantagesof such method is the conversion of metal catalyst into
their respective metal salts during synthesis and post

synthesis treatment [7], which increases the production
cost as well as raises the environmental issue.
In this paper, we describe the catalyst freesynthesis of carbon microspheres by the pyrolysis of awide range of plastic wastes collected from municipal
solid wastes including polypropylene (PP), high density
polyethylene (HDPE), low density polyethylene (LDPE),
polyacrylates (PC), polyvinyl chloride (PVC), polystyrene(PS) and PET under autogenic pressure. A single-stepsolvent free approach to obtain impurity free carbon
spheres using different plastic wastes as carbon sourceis explored.
The solid carbon spheres produced fromplastic wastes have been successfully utilized as thetemplate material for the synthesis of CuO hollow
microspheres with precipitation method.

2. Materials and Methods
2.1. Synthesis of carbon microspheresTypically, for the synthesis of carbon spheres,plastic material was taken in the stainless steel
autoclave. The autoclave was sealed and heated up todesired temperature at the heating rate of 20 °C/minutein the muffle furnace. The heating was cut off after
attaining the preset temperature and autoclave wasallowed to cool to room temperature. The product wascollected, washed with benzene and dried at 100 °C for
10 h in an air oven.
2.2 Fabrication of CuO hollow microspheres

7th International Symposium on Feedstock Recycling of Polymeric Materials (7th ISFR 2013)
New Delhi, India, 23-26 October 2013

0.1 g of CuCl2.2H2O (AR grade; S. d. finechem., India) mixed with 1.0 g of carbon spheres (PP700) was added in to 10 ml of Millipore water. 1.0 ml ofmethanol added in above mixture to dispersed carbon
spheres was ultra-sonicated for 1 hr. The mixture wasfurther sonicated after the addition of 1.0 ml of 0.1 M
NaOH for 15 min and aged at 80 °C for 6 hr. Filtered andwashed with excess of Millipore water followed by drying
at 100 °C for 5 hr in air oven. To obtain CuO hollow
spheres, the above core shell carbon sphere/CuO
particles were calcined in a muffle furnace at 600 °C for 2
h with the heating rate of 1 °C/min.

3. Results and Discussion

2. (a) CuO hollow spheres prepared using carbonspheres (PP-700) as template (inset electron diffraction
pattern of CuO hollow sphere); (b) surface of hollow
spheres composed with CuO nanoparticles; (c) building
block CuO nanoparticles observed in system and (d)crystal lattice of CuO nanoparticles
wall thickness of ~130 nm. CuO nanoparticles of ~25 nm
in size have also been observed along with microspheres(Fig. 2c). Inset of Fig. 2a showed the typical electron
diffraction pattern for CuO hollow microspheres whereas
Fig. 2d showed the crystal lattice of CuO microsphere.

4. Conclusions
Fig. 1. SEM images of carbon spheres produced bypyrolysis of different plastic materials under autogenicpressure; (a) PP-600, (b) PP-700, (c) PP-700-1, (d) PP800.
The formations of carbon spheres begin above
600 °C whereas an oily sticky mass was obtained below
600 °C. Even though the carbon spheres formation
begins at 600 °C, the obtained product consist ofagglomerated carbon spheres (Fig. 1a). The increase in
the reaction temperature from 600 °C to 700 °C
produces well dispersed carbon spheres with perfectspherical shape and smooth surface i.e. free from
amorphous carbon material (Fig. 1b). The further
increase in reaction time i.e. one hour at 700 °C (Fig. 1c)
as well as temperature (800 °C for zero time; Fig. 1d)
has no effect on the morphology and yield. On the basisof above observations, the reaction temperature and time
were selected as 700 °C and zero hour respectively, forfurther experiments with different plastic materials ascarbon precursor.
The carbon spheres were initially uniformly
coated with copper hydroxide under ultra-sonictreatment. To obtain the CuO hollow spheres the carbon
copper hydroxide core shell structure was calcined under
static atmosphere at 600 °C for 2 hr at the heating rate of
1 °C/min. The HR-TEM analysis (Fig. 2a) depicts theformation of CuO hollow microspheres by utilizing carbon
spheres as template. Fig. 2b shows the porous CuOhollow sphere composed of CuO nanoparticles with Fig.

The reported protocol allowed catalyst andsolvent free approach towards the large scale productionof carbon micro spheres using various plastic wastes.
Plastic materials such as PP, LDPE, HDPE and PC
resulted in the carbon spheres with 100% purity i.e.
absence of amorphous carbon material and foreign
morphologies. Without any post treatment, the obtainedcarbon spheres have been successfully utilized as thetemplate for the synthesis of nano crystalline CuO hollowspheres.

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7th International Symposium on Feedstock Recycling of Polymeric Materials (7th ISFR 2013)
New Delhi, India, 23-26 October 2013