Adding custom next/previous post buttons to WordPress

if ( ! function_exists( 'theme_content_navigation' ) ) {
    function theme_content_navigation( ) {
        global $wp_query;

        if ( $wp_query->max_num_pages > 1 ) { ?>
            <nav class="navigation" role="navigation">
                <div class="nav-previous"><?php next_posts_link( '' ); ?></div>
                <div class="nav-next"><?php previous_posts_link( '' ); ?></div>
            </nav>
        <?php 
        }
    }
}
add_action('wp_footer', 'theme_content_navigation');

reference link :

http://www.developerdrive.com/2013/07/adding-custom-nextprevious-post-buttons-to-wordpress-using-font-awesome/