I have a data frame with one column (col). I'm trying to remove duplicate records regardless of lowercase or Uppercase, for example

```
    df = pd.DataFrame({'Col': ['Appliance Identification', 'Natural Language','Social networks',
                                  'natural language', 'Personal robot', 'Social Networks', 'Natural language']})

```

output:

```
Col
0   Appliance Identification
1   Natural Language
2   Social networks
3   natural language
4   Personal robot
5   Social Networks
6   Natural language

```

Expected Output:

```
Col
0   Appliance Identification
1   Social networks
2   Personal robot
3   Natural language

```

How can this Dropping be done regardless of case-insensitively?